As someone who owns both a 360 and PS3, I'm torn on which system to get this game for.
I'm not an XBL subscriber (not willing to pay for something that should be free), so PS3 at least presents the possibility of playing the game online.
On the other hand, MUA was game that I bought alongside my PS3....and I'm very much afraid that Activision will keep the DLC exclusive to the 360 (particularly if the game ownership numbers skew heavily towards the 360).
Leaning towards picking this up on the 360, since that's where the active user base is. Also, as someone who used to use 'Hawkeye' as his Quake tag back in college, I'd hate to miss out on any of my favorite characters -- again -- because I bought the wrong version of the game. Being a fan of the old-school T-Bolts, I just know that at least one member of the team will be added later.