If you could be a Water, Air, Fire or Earth Bender, which one?

I'd almost certainly choose fire.
Though you can't create as you could with Earth or Water, it possesses and equal amount of creative/destructive power.

Destructive power yes. Just surround someone in flames (like a ball of fire) and eventually they will lose all Oxygen due to the fire and just die. Very deadly if thought out by all means.