Another vote for elementalist:
Each element has a specific aspect: Fire (AoE Damage), Water (Support and Healing), Air (Damage, mobility, minor control), Earth (dots, control, defense). It can switch at ease between each role (jump from damage to heal or to control, etc...). The only downside I can think of is being restricted to one weapon set (well, they have to, otherwise it would be quite OP) and squishy without building toward survivability.