I'd either be an earth kingdom, because I keep my cool and use logic in bad situations, or an air nomad because I am really good at avoiding trouble and don't really enjoy conflict until I'm in the thick of it.
Fire and water sound mixable to me, both can flow sort of. Lava bending sounds like a "bridge" bending ability. What would happen if an earth bender, who specialized in lava bending, was suddenly able to control flames???
Took a quiz and got earth nation which is cool because earth bending is my favorite. (It also helps that it leads into metal bending) Mainly because it looks like you're doing hard hitting karate moves when earth bending.