This has been my main competitive game since 2011. Back in vanilla MvC3, I played a bunch of teams, finally settling on Wesker/Dante/Magneto. It's a solid team comp, but it also had the added benefit of being able to DHC Glitch in any order.
Since UMvC3 came out, I've always ran some variation on the Dante/Rocket Raccoon shell. For my third character, I tried Iron Man, Hawkeye, and Magneto before finally settling on Vergil. Recently, I've been running Rocket Raccoon on point, as a lot of the common point characters that people play now (Zero, Morrigan, Magneto, Wolverine, Nova) tend to be too fast for Dante to fight with his really slow normals.
As a side note, if anybody wants to get into Marvel, or already plays the game and needs some feebdack or advice, I'd be happy to oblige.