Smash 4 has the most controversial clone characters added to the roster since the original implementation of clones in Melee. Between the over-representation of Fire Emblem chacters (at six), the multitude of sword-wielders (at thirteen), and inclusions like Dr. Mario and Dark Pit, people have given the Smash 4 roster a fair amount of shit.
I don't necessarily blame those people. But in the hopes of shedding some light on these problems, I'd like to take some time to discuss some of the key differences between Smash 4's various clones.
To start, we need to define a clone as well as another term: semi-clone. A clone is any character that shares all of their attack animations, including specials, with another character. It's not important which character is the "original", such that Marth is a clone of Lucina and Lucina is a clone of Marth, what's important is that the moveset is significantly similar. Semi-clones are definitely related, but have very different properties and maybe one or two drastically different special moves that share few if any properties. A classic example is Captain Falcon and Ganondorf. Movesets can differ between clones and semi-clones in many ways and can make the difference between a really good character and a really bad one. Other properties of the characters, besides the moveset, play a big role in setting them apart, like height or weight or ground, air, and fall speed. Most of these factors won't have a dramatic effect on casual play, but at the tournament level it makes a big difference. It's what puts Marth at the top and Roy down in the pits, in Melee for example.
Roy was pretty dramatically overhauled from his previous appearance in Melee, but Marth has largely stayed the same since his debut. Despite a shortened sword and some modifications to his neutral-B, Marth plays a lot like he always has and that means newcomer Lucina plays a lot like Marth as well. As one of the seemingly identical clone characters, Lucina came off as a pretty redundant addition to the cast, but there are a few things that make her stand apart from the old Melee standby.
Lucina lacks a tipper sweet-spot on her sword, that's probably the most dramatic difference and it dramatically effects how she operates at an optimal level. Whereas Marth gains a massive bonus to damage and knockback by landing a hit with the tip of his sword, Lucina's sword has its potency distributed evenly across her sword's hitbox. While she lacks the reward for good spacing that landing a tipper would provide, Lucina also won't suffer reduced effects of her attacks when fighting close. That means your spacing can be less precise and you won't be at a disadvantage against rush-down opponents that like to get in super close. Also, a few of her attacks (like her up-smash) are stronger regardless of the spacing of the attack. She's a less technical Marth, essentially.
Roy swings in the other direction, if Lucina is a balanced sword fighter and Marth requires more distance and set-ups, Roy succeeds by getting close and hammering away. His sword's sweet spot is at the hilt, just like in Melee, but unlike in Melee, Roy's moveset is optimized for that fact. It's pretty clear the original Marth/Roy moveset was designed originally with Marth in mind, whoes graceful long-reaching swings played well into spacing out attacks for a critical tipper. Roy couldn't pull that off in Melee since he was too busy trying to get up close to do any meaningful damage. Thankfully, in Smash 4, Roy's moveset was altered to speed up his swings and combo into his grabs. Roy is also the has the fastest aerial and fall speed among these three, and it works to keep him close to his opponents for fast follow-ups and tech chases. Although Marth is considered significantly less dangerous in Smash 4 compared to his Melee iteration, Roy has gone up in many people's estimations thanks to his modifications.
With Dr. Mario coming back from his hiatus, just like Roy, we now have the Mario clone fest of Melee back in action. Mario, as most people know, is meant to serve as a very neutral and balanced fighter in all of the Smash games. That means Luigi, since Melee, has been tweaked to represent a higher risk/reward playstyle versus Mario. Luigi's recovery is easily better than Mario's, but a lot trickier to pull off. While Mario lost his old Tornado down-B since Brawl, Mario's side-B Cape could be used to extend his recovery distance a small amount. Luigi, on the other hand, can launch his body horizontally with side-B (with a chance for a dramatic misfire), can climb a decent distance vertically with his up-B (but no horizontal distance), and can cover a lot of distance both horizontally and vertically with his down-B Tornado if you keep tapping the B button after use. Overall, Luigi has succeeded at tournament level far better than Mario ever has thanks to many of his attacks simply being much more potent. They require more skill to pull off, and his general floatiness can be its own challenge to control, but Luigi's attacks reward the skilled player far more than Mario ever can.
Which brings us to the black sheep of the trio. Dr. Mario has never been what anyone has considered to be "good". Although I have chosen to main the poor guy ever since Melee, I can recognize that Dr. Mario has some serious shortcomings even when compared to the middling performance of Mario. The trade off, and the reason I find him to be a fun character, is that Dr. Mario just operates in a different way to many of the other cast members. Whereas Mario excels at chaining together some basic combos, Dr. Mario is a lot better at punishing an opponent's mistakes. This essentially relies on playing against a bad player (or at least a player that's worse than you are) so this doesn't hold up too well at the tournament level where you'll be squaring off against people as good or better than you are. Regardless, if Dr. Mario gets the drop on you, he drops the whole load. While some of his attacks are a bit more powerful than Mario's, the key difference is in how those attacks connect and the trajectories they send you flying. In most cases, it's much worse to be hit by an equivalent attack of Dr. Mario's than Mario's. The problem is that this requires Dr. Mario to get his slow ass over to you and actually land a hit. He weighs a little more, but that just means he can get combo'd harder. His projectiles are slower and his Cape is narrower, his up-B covers less horizontal distance and his jump height is worse. But, he still has his old down-B tornado. It's a great tool for almost any situation, including during recovery, but it just isn't enough to rescue Doc from the doldrums.
Now, these guys are a classic semi-clone pair. With Falcon making his debut in the original Smash game, it was apparently decided that Ganon would only be able to make it into the game if they could cut some corners by fitting his moveset around Falcon's. The result is a weird representation of Ganondorf that doesn't make as much sense as Link or Zelda/Sheik's. Aside from how much sense his moves make for his character, Ganondorf is a load of fun to play in Smash 4.
The differences between these two characters should be easy to spot, as they would be between any semi-clones. Their special and normal moves share a lot of the same properties, but Ganon is tailored for raw power and Falcon is tailored for speed. In most cases, at higher level play, speed wins out over power. What's all that power good for if the speedy character never lets you land a single hit? The result is that Ganon has resided very close to the caboose of the official tier listings pretty much since his inception. A lot of good players out there have made some very good examples of what's possible with this character, but even the best rarely crack through to the top.
But the point about semi-clones is it makes more characters possible. As Sakurai pointed out before in the lead-up to Smash 4's release, the choice isn't between a unique character or a clone, it's between a clone character or no character. It just takes too much time to make a character from scratch.
I'll be honest, I had to look this one up. The differences between these two characters really takes the term "clone" to heart. All of their regular attacks, smash attacks, special attacks, and movement attributes are pretty much identical. My initial instinct was that people would suss out the finer differences as we gained familiarity with the game, but now that we have solid numbers on most things, it's pretty clear that Dark Pit is little more than a glorified costume swap for Pit (who actually has a dark color scheme to begin with).
Some differences do exist — it's not a total joke, at least. Dark Pit's neutral-B arrows can't be guided as much as Pit's, and Dark Pit's side-B attack sends opponents at an angle horizontally rather than upward like Pit's, making it a slightly better killing move. Other than that, they operate on a startlingly similar level. If all of the clones had this level of similarity between them, I'd be on the side of the people who groan at their inclusion. It probably doesn't help that I'm not, nor ever was, a fan of the Pit character in Smash. His movement and attacks never seemed to do it for me.
This is a classic duo that has undergone some changes to their relationship since Melee introduced us to Falco. Originally, Fox and Falco were designed with opposite killing moves. Fox has potent vertical kill potential and Falco had moves that worked better horizontally. Besides some movement speed and jump height changes, their movesets weren't too divergent. Since Brawl, however, this has seen some changes.
Fox has remained mostly the same in design since his Melee days, but Falco was given a bunch of weird multi-hit moves designed to carry his opponent across the screen instead of just having his attacks deal more knock back horizontally. In practice, this didn't quite work so well. In Brawl, which couldn't be patched, Falco struggled to keep his opponent from counter-attacking. And this wasn't helped by his poor ground and aerial speed, which kept him from being able to close with his oppnents. Low hitstun on most attacks in Brawl meant comboing was difficult to pull off at the best of times, so a character centered around comboing suffered a lot at high level play. Flash forward to Smash 4, and you've got a brighter picture for Falco. His moveset is largely the same except the hitstun and knocback have been adjusted so he can actually keep his targets where he needs them.
Fox, on the other hand, was hit rather soundly with a nerfing ever since Brawl. Long gone are his top-tier days thanks to massive delays added to his bread-and-butter attacks like his reflector and his up-smash. Fast characters generally excel at high level play, but only if they can secure a kill. Fox continues struggle in that regard even in the more combo-friendly Smash 4 where his approach game still has serious flaws and his old killing moves still have very punishable ending lag. The old idea of horizontal versus vertical play style isn't really preserved much in Smash 4 between these two, since they're both relatively capable of KO'ing in either direction even at lower levels of play. Falco has simply adopted a slower aerial combo game whereas Fox has retained a quick but strong plan of attack. Unfortunately, neither are particularly amazing at their jobs, and haven't seen regular tournament wins outside of Melee.
This pairing is an interesting one, and does a good job of exploring potential differences in their shared moveset. They both embody roughly the same style and goal of approach. Lucas sports a few more heavy hitting high-risk smash attacks, and a tether grab, but both are grab-oriented aerial combo characters with a strong projectile game and a tricky recovery.
Their special attacks cause different kinds of knockback and therefore open up different windows for follow ups, but both sets are equally good. Both use grab setups for aerial attacks and, at higher percents, their grabs are easily killing throws. Lucas might have a slight advantage as his neutral-B is a bit easier to land. It can freeze opponents if it hits, instead of just applying a ton of damage and knockback, and can be moved more quickly. Neither have great neutral-B's, but that's more than made up for their side-B, PK Fire. Ness's locks opponents in place, generally a setup for a grab, while Lucas's deals a clean knockback. Both are amazing spacing tools, just like the up-B PK Thunder attacks which differ only slightly in their properties.
Generally, they both get to about the same place with their movesets, just by different means. It's not quite like any other clone pairing, not even Lucina and Marth, to operate on such a similar level while having significantly different attack properties.
So I think that should about wrap it up! Hopefully it wasn't too long, or you were content to skip to the characters you were interested in. I may have missed some key facts here and there, or messed up some information. Most of this is coming from my own experience and not any online resource, so feel free to add corrections in the comments!