X-Men, pretty easy in my opinion.
Shimmer should be taken out by cyclops early in the fight without anyone getting to close, else she could be dangerous. I don't think psimon is a match for emma. I think colussus is stronger then Mammoth, in any case he can hold his own till cyclops helps him. Gizmo will have his hands full with wolverine or beast.
The only one i can see as a threath is Jinx. But with her team gone i doubt she could do anything back :)
So i'll go for the X-men
That would infuence the battle. If shimmer would stay close to Mammoth, i think they have a good chance of taking colussus, beast and wolverine because they have to get close to do damage. Mammoth could take them out when they have no powers.
So it's a tough one, but i still feel emma has better telepathic powers and could take some out before they could react. Because don't forget, the other team doesn't know her either. I think it comes down to Shimmer really, she can be an amazing threath when ignored.
But The X-Men win-
The Fearsome 5 are all very powerful and pound for pound except for Gizmo more powerrful than a single X-men, the DC comics power scale is just higher than Marvel's.
But They don't fight well as a team and that is where they will get skilled.
Psimon can resist Emma but he won't use his powers to help shield the mind of weak willed dumb as a brick Mammoth.
Wolverine (Always Overrated) in this fight plays spoiler he jumps in on Mammoth and Draws everyones fire. During that short fight (Shimmer converts his metal bones to phospherous or something) beast and Cyclops learn what the 5 can do.
Kitty Walks through Gizmo, taking him down.
Cyclops snipes Shimmer and Jinx , he may only get one though but that's all they need.
Beast occupies Mammoth with bouncing about and big words/insults . Pitor locks of Mammoth in an arm lock till Mammoth breaks his own Armor worse.
IIf Shimmer or Jinx is left Kitty walks up to one takes their hand and phases them till they run out of breath (You can't breath while phaseing and kitty has trained at holding her breath)
Psimon is left and is in a dead lok with Emma..Beast punches him in the face...game over