Who are the best 'healer' hero's
It depends what your interpretation of "best" is.
In insane dungeons, Ghoulem can mess you up by taking away PD procs.
In Mesa 4 (beginners first time using it) Orksbane can be brilliant.
each healer has their uses, if youre asking what the mot versatile healer is, then hands down its Ghoulem
Ghoulem is probably the best healer, but.... Druid also has a damage buff, that is stackable. This is why you will see many of the top players with Devo Druids. Druid is very useful in game modes like Archdemon, where the damage buff can stack many times. Eventually you'll want both completely leveled up.