If we are going off of lore I'd say it's a toss up between BLM, WHM, and SMN. If we are going off of in game ability then DNC, SMN, BLM, RPR. IIRC DNC doesn't actually have the crazy AOE power they do in game as they are primarily about buffing spirits of allies. BLM and WHM both have the reputation in game of completely ruining the area they fight in because they draw Aether from around them. This is not only really powerful in huge battles for raw destruction but also in terms of a drawn out fight you can basically make the area your enemy resides in horrendous to live in. I say RPR based on in game stuff because of the aoe soul siphon ability. They would essentially have endless resource the more people die around them. Considering they are usually assassins in lore I don't think that would carry over