I will say, having done this a few times, fire, water and air are usually the most popular choices. Earth is last but is definitely not least (there may or not be an NPC that I love in the world that is an Earth Bender) and there is always a vote for a non-bender which is a pleasant surprise to me. I'm always excited to see what comes of it.

Any particular reason why you're choosing the element(s) you two are?