Ok, this has kinda been done in the 80’s, but we haven’t had any rematches so.....5 on 5 First Round
Titans (Mostly Original Team, Taking Heroes in Crisis into account)
Nightwing (Dick Grayson)
Troia (Donna Troy)
Tempest (Garth)
Omen (Lilith Clay, If Writers would rather use her instead of Wally and Roy, in light of recent events)
Bumblebee (Karen Duncan)

Vs
X-Men (Original Team, assuming fight happens after AoX/ HOX/ POX, or just use a world close enough to 616)
Cyclops (Scott Summers)
Phoenix (Jean Grey Summers)
Beast (Hank McCoy)
Iceman (Bobby Drake)
Archangel (Warren Worthington the Third)