I'd probably have to go with the Alpha series out of the choices, because I totally loved Alpha 2 as a kid. I still love Street Fighter, but I play Capcom vs SNK 2 and Marvel vs Capcom 2 more than anything. 2D fighters are great, but I really suck at them--I can beat most of my friends, but when it comes to any complex combos over the simplest moves, I'm worthless.
I'm super psyched for Super Street Fighter II HD Remix and Super Puzzle Fighter II HD.