Well, with fire you don't ever have to be near some source of fire to bend it. It comes out of your hands and feet. With water you have to be near a source to bend it. And also with fire, I can electrocute things. Thats how Mako took down Ming-Hua in the last episode. So water is now
All of them were my favorite at one point except earth... I dont know why I have nthing against Earth its just that if I could pick i would be something else. Its just the most boring out of them. Water is awesome cause of bloodbending healing ice and steam and all of the things you can do. Fire is just plain awesome like fwoosh fwoosh.
Air is pretty good cause of the variety of moves and you can getnit from anywhere. Right now I would have to say FIREEEEE