In Aspect of Assault and without any disruption the Melee Healer deals more damage (has more dps). But in most boss fight you have to move a lot, and mostly away from the boss, in this case you can't use your maximum potential. So in these situations maybe the Caster Healer is the better option, because you are already far from the boss and there is less danger there, so you can do anything without too much problem.
In my opinion the Full Healer is good. With a lot of Brutality and a decent amount of Double Attack you can heal anything at the moment, but only with a lot of attention.