Excalibur plus!
Kitty, Kurt, Rachel, Captain Britain or Brian in whatever identity he prefers, Megan because you can't have him without her (and I count her an X-Man).
Then Ice Man and Firestar because nostalgia and the characters are usually fun.
Dazzler, Magik, Blink to round it out.
But, those last three could be switched out in any combination with Beak, Madrox, and/or Storm and I'd be okay with it.
Assuming that I was a writer rather than the reader, I'd want to include two of my own ideas in the team instead of the later listed characters.
10 versions of Morph from all around the multiverse.
No wait, 8 Morphs, Forge to make them tech goodies, and Jamie Madrox for one-man zerg rushes.
Iceman
Shadowcat
Storm
White Queen
Fantomex
Vulcan
Forge
Cable
Magik
Magneto
