I'd likely be a Firebender, as I consider my element to be fire in general. Though honestly, it'd kind of suck to be one. It's not really as useful as the other three, and more serves for harming and warlike purposes. As seen from a few episodes of the series, Firebending is very dangerous. If you're not careful and well-disciplined, you can get burned and harm others. I'd probably want to learn from a master first to get my abilities in line first. I wouldn't even touch lightning bending though.
After I learned, I'd try to put them to good use. Maybe somebody has an old-fashioned stove? Fire girl to the rescue! There's a black out? Let's power the house using fire! It's totally freezing here? Don't worry, I'll make a fire! Though likely, I'd just casually be roasting random foods and eating them most of the time if I could Firebend. It'd certainly help me get more into cooking. (I'd also fireproof my house just in case)