What 3 class group is best?

[Loke]

Cleric + enchanter + whatever. Add another caster or pet class if you don't want to deal with melees, or a monk which would probably be the best melee to add in that trio. Shaman can add dots, malo, another slower. Mages and necros give a pet that can take over if chanter charm pet breaks. Druid and wiz add caster dps and transportation. Basically, a cleric and a chanter are the foundation of any solid group, so having both of them really sets you up for any grouping situation you might find yourself in.