Both because Alice would take care of her and make sure she looks good and Rosalie would take the mothering so both of the cambined would be one awesome godmother!
I think Alice would make a way better godmother for Renesmee and i think that Bella would pick her. But Rosalie does do a lot for Renesmee..so maybe both.
BOTH! How could you choose?! Rose would be like a second mother of sorts, and Alice would be the fashion designer. Both a must-have!!!