Xadem said: 

so which element would you guys want to master

I feel like Earth Bending is handled too rigidly in the show, save for a few expressions of it as Legend of Korra goes on. 

I wish Sand Bending was explored a little more. Much like how Water Bending could be used to control plant life, sand has a lot of potential. It's basically air bending with it's opposing element. Converting Earth to Sand and using it to pull people into pit traps, building custom terrain, Earth Bending is highly underrated. 

I also feel like Earth Bending is how you could get closer to pulling some Magneto strategies, like pulling the metal out of someone's body, or reshaping a piece of metal that's on your person ala Full Metal Alchemist. Imagine an inventor who could bend metal for example and you have some odd applications of bending at your fingertips.