Having two blasters (for example, Magneto) and two brawlers (for example, Wolverine) works well. The following team is highly useful, because there are times where you will need a mutant with super strength to move an object out of the way. If you need a bridge formed, use Magneto. If you need a flyer, both Magneto and Ironman can fill that role. The heavy metal group is Colossus, Juggernaut, Ironman and Magneto.