If you got mad skills than go with the 2 spriests and an affliction lock. If not, and you're just learning, than go with 3 elemental shaman and go for the Ol' lightning bolt - flame shock-instant lava burst kills on lesser geared opponents.

Don't expect much out of either team because in 3's if you get one character crowd controlled, and you almost always will, you will not have enough burst to kill anything with resil. For the dot team, I believe if played very well they can have a lot of success simply draining teams through massive dots, crowd control, and running away from trouble. Though, you'll still lose to smart teams no matter how much you outplay them.