This was a tough choice, but I voted for my girl, Monet. If anything, I want to see how Everett synch up with Monet and see how he uses the Penance form.
Lots of great choices, but Firestar would be redundant with Sunfire on the team, I've never found Siryn to be too interesting, I don't give a eff about Micromax. Gorgon doesn't seem like he would fit and Bling needs more experience. I could go with Surge or Armor, but chose Penance. I wanted Gentle, but he's not dynamic enough for the X-Men squad.
But, in all seriousness. Monet as a badass in House of X 4. She died fighting with NO hesitation was one of the first on the battlefield in Otherworld in X of Swords. Monet is ride or die and I want her on The X-Men.