I don't think we are going to get an accurate sample of what are the best party compositions right now. The AI 2.0 update completely broke the game in terms of allowing the player to have several viable options. So right now, it's stack crowed control and Will(initiative) just to stand the chance of surviving more than a round or two, ruling out many class options for your companions. If you don't take out or CC one or two enemies in the first round(or you have low initiative and you have to wait for 2 enemies to go first) you have already lost, often because you entire team, even if spread out manually, will be stuned/knocked down/sitting at 10% life before you even have a chance to move.
When they tweak the numbers a bit, I think we will see things more clearly.
Explorer difficulty could be a whole nother story though.
