Air, you will speed yourself and your party members up, as well as cause interrupts to enemy spells. You may decide to choose more than one element, but this is not recommended because of attribute points and
power leveling armor upgrades. Arguably, it is easier to have a fire ele, and is certainly the most popular for damage. Earth is most used for farming (playing solo to get maximum
power leveling & items), air is useful for running (going solo from one location to another) and in Alliance Battles, and water is very seldom used for anything.