I like them both for different reasons.
I like Renesmee because it unites the Cullens and the Swans as a family and in a way solidifies the family bond between Edward and Bella.
I like Nessie because it is the first real sign of Jacob becoming welcome and a part of the family. It also allows Renesmee to take on the fake name of Vanessa, although this is not ultimately required.
I sorta agree with Bella's reaction.
When I first read "Nessie" I was like what the heck!
I don't really like it, but I agree with the other person. It allows Jake to be apart of the family and it later gives Renesme the alias Vanessa.