Well since warrior already has buffs to tank for 45 seconds, I think cleric won't be needed (I guess you only want it for defence and hp recovery?). So I'd say warlock for the debuffs, but remember: casting warlock spells could make you run out of mp..
Depends on what you want.
- High Damage - take warrior/warlock for the debuffs. - High Defence - take warrior/cleric for bless spell. - Average Damage and Defence - take wizard/cleric.