X-Men
Keep
Archangel - I'm going to assume that 'Archangel' is his death form after Apocalypse, not his current 'Angel' feathery self.
Banshee
Beast
Bishop
Cable (Burnt Offering) - His powers were at his strongest at that point.  This may be too powerful though
Cannonball
Chamber (Pre M-Day)
Charles Xavier (Pre M-Day) - Just for the sake of it, we should have him during New X-Men so that he can walk and run and all that
Colossus
Cyclops
Dazzler
Emma Frost
Forge
Gambit - I wouldn't mind having him when he had his full powers during his first ongoing, so that he could charge things on sight, organic and non-organic
Havoc
Iceman - I'd be cool to have his 'X-Men Forever' version, where he has complete control of his body to a molecular level, where he can even turn to mist or water
Jean Grey
Joseph
Juggernaut - Do we want X-Man or his majorly tough villain days
Kitty Pryde
Lifeguard
Marrow
Nightcrawler
Northstar - X-Man or Agent of Hydra?
Polaris - Crazy? X-Factor? current Pestilance?
Psylocke (Crimson Dawn) - This version has both telepathy, telekinesis, and her shadow powers
Rachel Grey - WE can go with current more experienced Rachel or Pre-Phoenix Rachel with less experience but more ruthless
Rogue - Do we want her curant flame version, the original Ms. Marvel version, or the one that could call up powers at will?
Stacey X (Pre M-Day)
Storm
Sunfire (Famine) - Nothing taken away from the character, but he's more ruthless and make people desperately starved.
Thunderbird III
Wolverine
X-23
Drop
Cecelia Reyes - While she can be offensive, she's mostly defensive and wouldn't make it far I don't think.
Jubilee - She could possibly do well, but I do see her advancing
Maggott - Good character, but he's too limited
Mimic - I'd rather have the Exiles counterpart
Sage - Dues Ex Machina who's powers are all over the place.  I'd rather go without her.
Slipstream - He's just a teleport her, no offensive fighting experience
Thunderbird I - We already have the Exiles counterpart
Xorn II - Again, Dues Ex Machina who doesn't wish to fight.  I don't see him going far really.
Not Sure
Husk - I want Husk in this thing, but if we only have one version I think I'd rather have her AoA counterpart
Longshot - His powers may be a bit too unpredictable.  Thoughts?
Revanche - Love her but we already have Psylocke... do we need a second?
Potentials
There shouldn't be any, as I used every person that was ever an X-Man, with the exception of Paulie Provenzano, Wraith, Sunpyre, and Fitz (or whatever that skrull from the Twelve storyline was) and all of them can be left out with no problem.  Sunpyre's just like Sunfire, there's better skrulls than Fitz, Wraith was lame, and while Paulie could have had potential, he has no offensive training.
Wait... is Nate Grey on the other X-Character list?  If not then he needs added.