Nessie is way better that Renesmee. and I'm not just saying that because my name is Vannessa and I've been nick named Nessie/Nessa. I think it's really cute and it suite the character.
Well If im *writeing or typeing about her, then I say Nessie. But if i *talk about her, then I say Renesmee!
Plus Renesmee is very oringinal, and Nessie makes her sound like a little monster...which...I guess she sorta is, but yea. :) Thats how *I see it anyway. :)