Tank: war and drk are both as easy as each other
Healer: Whm, sch used to be easier but ocd fairy skills made it a pain to play, whm healing is also all instant now unless you're bad enough to use cure or medica 2
Melee: drg, no variances baby rotation, just don't drop your eyes on the floor during downtime
Ranged: mch, the wardrk of ranged, except only easier, 1-2-3, spam heat blast 5 times, only "difficulty" of it is using drill and anchor on cd, which is a joke
Caster: smn, infinite mobility and pressing triple weaving isn't hard