Personally, I've seen all types of nipples and loved every type. The only thing I hope for in a nipple is that it actually does something for the girl.
Some girls just don't get anything out of nipple play and that can be disappointing and a little awkward if you are having the time of your life and all she's thinking about is how to get you to move on to another part of her.
It's really hot to find a girl that really gets off on some nipple action.
KC