Interesting question.
I've already thought about girl, and I know that one easily.
As for a boy, though. . .More difficult to think about.
Girl: Ty Lee. Toph was an option, but she comes up to what, my hip? Short girls aren't my thing. Katara's to nice, Azula's to agressive, Mai's . . not my type at all, and none of the other girls even stick out. Ty Lee is strong enough to protect herself, but still retains that nice, innocent aura. She's loyal, and behind that nice mask you know she'd be able to kick your a** if you ******** with her the wrong way.
Boy: I guess Sokka, really. Protective guys are adorable, and the Humor is a plus. Someone who would cherish you, protect you, and make you laugh the whole time? What's not to like?