I really have loved all the Warriors games I've played on 360. I've played DW5 Empires, SW2, SW2 Empires, DW6, and Warriors Orochi. So Gundam is the only one I haven't played.
My favorite of the ones I've played was definitely Warriors Orochi. The 3 character system, plus the weapon fusion system really made it the meatiest feeling. The storyline was pretty lame, but fun anyway.