I’m going with terra. Also, this is a question that I just thought about, but can terra control ice?

No, she can't.

@Heartless Frost good to know.

I'll go with Mera as along with her powerful hydrokonesis I would also gain her atlantean physiology and Sorcery.

With her Sorcery she can cast spells plus her atlantean physiology I'll have super strength and durability also breathing underwater while Terra I just move rocks

With Mera's powers, I'd be an Atlantean on top of being a Waterbender. Whereas with Terra, I'd be an Earthbender and nothing else, as she literally has nothing else going for her.