Emacs is far easier to script and plays nicer with other programs so there are more, more useful extensions for working in various languages. On the other hand, I find vim's modal interface faster and easier on my hands than emac's chording interface. viper-mode in emacs might be ideal.
(Disclaimer: I do use Emacs, mostly.)
Haven't tried learning the keybindings yet myself, and I've heard VIPER isn't the complete Vim.
It amuses me that people actually think that's just a joke.
Ergonomics. There's an emacs key chord for everything, but many of them involve two or three modifier keys.
i.e. search and replace is Alt+Shift+5, indent block is Ctrl+Alt+\
These require some finger contortions. I haven't used vim, but the impression I get is that similar commands in vim are all closer to home row so you don't have to contort your hands as much.
search & replace is % indent is > (auto-indent is =)
Emacs seems really neat, and I'd like to try out some other editors, but none of them compare to the ease of vim's modal style.