I used Aquamacs for a while, but reverted to Carbon emacs, because it was easier to make similar to emacs on Linux that I also use regularly. If you don't use emacs anywhere else, Aquamacs would be fine, I think.
I use the exact same Emacs environment on my mac with Carbon Emacs as I use on Unix systems and my windows machine at work. I can't speak for the unportability of Aquamacs, but Carbon Emacs works exactly as I expect so good 'nuff!