I think wind because it has the potential to overpower all the other elements, including fire.

Without oxygen (and thus, wind), fire cannot exist, and to end fire, all you'd have to do is make a area void of any and all wid/air.

The wind can push the water away.

With enough wind and power/speed behind it, the wind can move mountains, or any other earthly thing.

And without it, we'd all be dead!