I have WAR/DRG at i90, PLD/BRD at i87,and what class did i learn the most from playing? My SCH. Because now i know how hard it really is to do some of the things. So i know more appropriately when i gotta hit CD's or when i can expect to receive less healing because of mechanics.

Besides that, melee DPS would be best to learn from. Doesn't take too long playing a MNK/DRG before you realize that they'll want you to do ur best keeping the rear and flank of the boss available to them. And they don't want to see the front either, it's gonna hurt.