MacVim works well and certainly looks more mature than Vim-Cocoa, moreover there is a Cocoa plugin architecture in the pipeline for MacVim (and someone is already working on a TextMate style file browser tray plugin which is a huge ++ IMHO).
There was also a Carbon version of Vim, but this didn't offer a great deal over the Terminal version. i.e. only allowed one window open, not very OSX in appearence...
Aquamacs is very usable and looks pretty good. Supports both traditional Mac OS style keyboard shortcuts (command-O, command-S) and the Control/Meta shortcuts for those raised on traditional Emacs. It is definitely more Mac-like than Carbon Emacs. It seems stable and fast, but I am not an Emacs guru so I don't stress it all that much when I use it. I can't speak to the extensiveness of the included elisp packages, either.
Someone syncs Carbon Emacs with the upstream tree quarterly I think. Aquamacs has a more irregular schedule, but it's seen some pretty major updates over the last year.