I’d say UMvC3. There’s room for more variety than in Infinite.
For all the talk about how freeing the tags make combos, there’s always that one thing about it that all the pros and online warriors are doing, and currently, that’s locking people down with a move and then tagging for mix ups. It wouldn’t be so bad if everyone had a different way to do this, but at the current meta, not everyone does. Those that do, all do it the same way.
Infinite also seems to reward yolo play more than calculated play. UMvC3 also made braindead yolo play possible, but it could have easily gone wrong. Infinite makes it really easy to do extremely unsafe moves, as you can just tag to make it safe. In UMvC3, making an unsafe move safe cost a bar or sometimes meant calling an assist beforehand (which is telegraphed) which btw, could also cost you your assist character (and maybe also your point) if your opponent punished that properly.
If you want to be good in Infinite, just pick characters that can lockdown your opponent for a tagged in character.
If you want to be good in UMvC3, you can be all braindead rushdown with Wolverine/Doom/Vergil. Or you could try Morrigan/Doom/Vergil to pull off ridiculous Bullet Hell, which you had to practice to pull off, otherwise, decent counter teams would give you hell. If you practiced, decent counter teams would give you a fun challenge. Maybe Zero May cry is up your alley, as cheap as it is, you also had to know what you were doing to an extent.
If neither of these top tier teams are your style, you could put together other decent teams that may not be top tier cheap, but could still put in some work.
Winning in UMvC3 was rewarding and felt fun if the opponent was just as good you were and played with a different playstyle and team.
Winning in Infinite feels like you’re just going through the motions.
Just my opinion,