Back on topic - to answer your question.
2s:
DPS - Frost mage, sub rogue, affli lock, mm hunter
Heal - DPri, Rdudu, MW Monk, Hpala
3s:
DPS - Affli lock, frost mage, shadow priest, mm hunter, sub rogue
Heal - Rdudu, Rsham, Hpala
Of course it's not talking about certain comps where certain classes will work extremely well but generally the classes I mentioned are best in the mentioned environments.