CAPCOM
-Replace Akuma with Megaman.
Megaman is the ICON of Capcom, and not having him in is a fucking insult. And Akuma is a clone of Ryu. The face of Capcom, or a Ryu clone? Easy choice.
-C. Viper with Strider
As for Viper: I get it. Trying to put one of the new characters up in one of the big games. But it just seems a little too... forced. I wasn't one of the ones bitching about Strider not being in it, but putting him back would be nice.
MARVEL
-Replace Sentinel with Bullseye or Daredevil.
I fucking HATE Sentinel. It's just as OP as ever, with any problems they tried to take care of being overshadowed by how much he owns in X-Factor. Seriously everyone puts Sentinel on their team, and saves him for last, using X-Factor to completly RAPE. Plus, Bullseye would just be awesome. Hell, it wouldn't be too hard. Make the fighting style a fusion of Hsien-Ko, Arthur and MvC2's Gambit. As for DD, just as awesome.
All things considered, the roster is actually pretty good. A little too many X-Men, but not that bad.
I'm assumine Frank West will eventually be DLC. Maybe not the first wave, but he'll get in eventually.
BONUS HIDDEN CHARACTER:
Scrooge McDuck! Think about it: He was in a classic Capcom game, and is owned by Disney, who owns Marvel!