Both possible low level affixes are the key killers for tanks. They raise the health of either the boss or the trash, not good for a low dps team.

That being said, any composition seems to be able to do about the same. I have had no trouble doing +3s with all tanks, all melee dps, all hunters, trinity, heal+4 dps, etc. I have tried a lot.

In summary, I think you will regret something no matter what you try, but anything you choose is going to get you just as far.

Have fun!!