So we've got...
The Avengers entire roster sans X-related people. Do honorary Avengers count, like the Guardians of the Galaxy?
Thunderbolts
New Warriors
Fantastic Four
Invaders
and the Defenders (sans Surfer I'm supposing)
Marvel Earth would take it, yes the X-Men have some heavy hitters with Cable and X-Man, but last I checked Genis-Vell had adopted Earth as his base of operations and had hunkered down with the T-bolts. He and the Sentry could put a large hole in the X group, IMO.
giant man wouldnt do mutch
Yes he would. His strengths have never really been in physical confrontation, but he makes one hell of an addition to a think tank. The X-Men have Beast, Forge, Xavier, Magneto, Bishop and Cable (knowledge of future tech would put them into a think tank). While the other force has Reed Richards, Pym, Tony Stark, T'Challa, Fixer, Zemo, Black Knight, Vision, Lang (unless you want him dead), Red Raven, Thin Man. I'd go with Marvel Earth in regards to brain power.