I think it was KT that said the 3 team leaders will be Jean, Storm, & Armor. Going by preview art alone, I'd say their groups breakdown like this:
Jean, Bishop, X-23, & Northstar
Storm, Nightcrawler, Psylocke, Jubilee, & Cannonball
Armor, Pixie, Rockslide, Glob, & Anole
Believe Beast, Iceman, & Oya, have only been shown in non-combat situations, so far.