Shaman is an obvious choice for the slows, heals, and buffs.
However, you might want to toy around with a beastlord as the other choice. They can slow and buff (though not as well as the shaman). They can also do light healing (though nowhere near as much as the true healing classes). The advantages that they have over the shaman is considerably more DPS, and they can have the offtanking pet. The healing isn't necessarily as crucial either because you can lifetap with the SK, and the mob dies much faster with the significantly better DPS.
As always, there is never any true "right" answer, it boils down to what class you enjoy more.