IMO:
Adventurer>everything and everyone else. Cause:
1) Clawyn and Ruksana are good damage-dealers, but require build-up of their TP and are fragile as fuck;
2) other physical damage dealers suck, plain and simple;
3) mages are slow (sometimes act after enemies), fragile, only Meredith has reliable damaging spell (Cinder Burst - high damage, line-AOE that hits everything 99,9% of times);
while:
4) protag has humongous health-pool, his or her survivability dwarfs anyone else's, especially on Guardian and Adventurer classes;
5) Adventurer (and few other classes) can equip swords and Eraser is the best weapon in the game damage-wise (500 ATK) and it is a sword;
which means:
6) Adventurer lives longer than most classes while having one of the best damage outputs at the same time, meaning this class will most likely outdamage anything and anyone in your party.