Emacs versus Vim. It’s an always entertaining argument and we all have fun with it from time to time. My own views, as I’ve expressed often on Irreal, are that they’re both really good editors and the editors of choice for most serious, topnotch developers.
There is, to my mind, a difference: If you want a fast simple editor that does one thing well, Vim is probably your best bet. If you want a programming/editing platform that provides a framework that allows you to build the perfect (for you) editing and workflow environment, Emacs is probably the right choice.
Chris Siebenmann has a post that approaches the problem from the point of view of someone conversant in both. Although he appears to be most comfortable in Emacs, he’s been using Vim a lot and likes it. He’s been wondering if he should switch to Vim and be done with it. At the end of the day, he chose to remain with Emacs for the same sort of reasons that I expressed above: Emacs is so easily configurable and there are so many 3rd party packages for it that it seemed like a better choice for him.
Be sure to take a look at his post to get his unfiltered opinions on the subject. I can only say that I came to Emacs (from Vim) because of the Lisp integration (Slime, etc.) and stayed because it provides me with a wonderful, flexible, work environment.