I'd like to jump in and say that I prefer straight handles. I used to buy handles with bellies and carved ends similar to what NH is describing from the hardware stores when I was younger. Then I started making my own handles and gradually moved to a straight handle(I still make a handle with a carved end). The main advantage of the straight handle is that you can hold the handle any distance from the axehead and the handle is consistent... I personally feel more accurate with a straight handle, but that is what I'm used to now.
Just my 2 cents.