Druids and paladins are good (I. E. Forgiving) melee choices IMO as they can be tank, dps or heals. Double bonus is you can queue with them with off spec covering the three roles.

Also, I would go non-mixed as it is easier to manage and learn.

That said, I'm not the bleeding edge type so some of the folks that run raids or heroics regularly may have more information that is relevant to you.