If you want quick xp for a battle class, escort leves (the ones that make you /beckon) are great. Make sure to do ones that are level appropriate (like Costa del Sol at 30, Wineport at 35, etc) and max out their difficulty. Put the /beckon command on a bar and continue to use it as you walk towards the destination. You can ignore the mobs on the way, just keep pulling the escort NPC to the area to finish.

With the leve in Costa del Sol you can finish it in approximately a minute and gain about 11,500 xp. This is just as good as FATEs in the area. The level 35 ones jump up to about 14,000 xp. You can do about 4 of these in a row before you have to do another leve (possibly 2) to refresh the leve list and rinse and repeat.

Leves are of course a limited resource, but if you're trying to level up a class, this is something you can do in between solo DF queues, or just something to do when you have nothing better to do. You can of course group up with other people and all do it together if you choose.