I agree with most of what others say about each game teaching something.
Although SF4… I’ve never been a fan of. I don’t like the things that SF4 adds to the fundamentals. I don’t know if people are still on the “hate” train but I honestly prefer SFxT. You learn most the same fundamentals, except the game is nowhere near as focused on Vortex and Focus Attacks (both things I feel detract from the fighting game fundamentals). I’d say strong fundamentals are even more important in SFxT to be honest.
UMvC - This game will get you to be incredible at defense. It’s also very complex, and very fast, compared to other fighting games. While it’s a bit cheaper and more random than other games, it will teach you great skills overall.
P4A - I agree with others said about this title. It’s very strong at teaching the fighting game fundamentals, along with SF4/SFxT, but it’s a very different pace and I feel requires a bit more defense than the other games as well. Sort of combining the strengths of SF games and UMvC. Learning different paces for the same fundamentals will be great as a player overall, and probably teach you a few new things that weren’t as apparent while you were learning other games.
MK - I’m mixed about this title. I love the mobility moves, and some characters are quite fun. But I’ve never liked the lack of mixups, and I feel the characters are just too… basic. After just a couple hours with each character you know basically everything there is to learn about a character. I didn’t like that feeling. I don’t know how much this game will teach you relative to other games for this reason - sure it has footsies and some of the same fundamentals, but I can’t think of anything that this game will teach you that a SF game or P4A won’t teach you better. I’m hoping Injustice fixes these issues with MK.
Tekken 6 - This is a different ballgame imo. I keep 3d fighters separate from 2d fighters. They play way different, Tekken in particular, is so focused on momentum. I don’t enjoy that for a competitive game, fights are over too fast and usually too 1 sided for my taste. But if you are going to play a 3d fighter, I’d say TTT2 or VF are your best bet (depending on the type of player you are).
Honestly that choice is up to you. If you had to put them in order, which games do you enjoy playing from most to least?
From the games mentioned I feel SF or SFxT, P4A, and UMvC could teach you the most about 2d fighters. The SF games are most about fundamentals rather than combos, UMvC is more about combos + high speed + incredible offense and defense. P4A is in the middle between SF and UMvC where it shares the elements of both without a major focus on either.
My games of choice right now are SFxT (especially with the new patch coming out) and P4A. The only reason UMvC is not in the mix is because the netcode isn’t up to par and a lot of my time is spent online. P4A and SFxT both have very playable netcode so that leaves them in the mix.
Take from that what you will, and add your favorite rankings to the mix, and hopefully that gives you some guidance!