[Atmas]

Cleric, Enchanter, Knight, and Flex.
Cleric + Enchanter is already a great duo. Knight snap agro plus other utilities set them so far ahead of warrior it's ridiculous for a group. Knight pulls with FDs/Lulls/Roots and snares are also miles ahead if you don't get a monk or want to put all the work on the enchanter.

The cohesiveness of those 3 can't be understated. Knights benefit from both the mana regen and haste buffs of enchanter. They have snap agro making the cleric healing more efficient and do an infinitely better job of helping the enchanter with pet breaks.

The 4th member could be whatever there are different benefits to members like monk, rogue, necro, etc. I probably wouldn't do a shaman in this comp.

There are some alternative comps with shaman/druid healing and other tanking like warrior, monk, or ranger. You can play them if you enjoy the classes, they just probably won't be as efficient but playing what you like is best in the long run for having fun.