I use mostly Jean, Magma, Rogue, and Wolverine. But depending on the enemies I'm expecting I'll switch it up. Like when I was fighting the Sentinels in New York, I used Rogue, Colossus, and Wolverine. Iceman was my fourth once I realized the Sentinels go down a lot faster if you freeze them first.

Right now I'm rescuing the Professor from the astral plane. I'm having trouble beating Avalanche.