Right up front: I do not want to start a religious war.
I've used vi for as long as I can remember, and the few times I've tried to pick up Emacs I've been so lost that I've quickly given up. Lots of people find Emacs very powerful, however. Its programmability is somewhat legendary. I'm primarily doing Solaris+Java development, and I'd like to ask a simple question: will my productivity increase if I invest time in getting my head around Emacs? Is the functionality that it offers over Vim going to be paid back in productivity increases in a reasonable timeframe?
Repeat: I don't want a "my editor is better than yours" answer. I just want a yes or no answer as to whether it's worth investing the time or not. Will my productivity really increase?
[Disclaimer: personally, I prefer Vim. Disclaimer disclaimer: read on.]
Vim excels in the small: by making motion and action separate concepts and providing facilities for complex repeats, you can perform incredibly powerful editing operations in just a short sequence of keystrokes. You can easily do things in Vim in the normal course of editing that would require you to drop down to scripting in Emacs. Also, most of the power you use comes out of the box, so even if you have extensive .vimrc
customisations, chances are you will be able to work productively with any Vim installation.
Emacs excels in the large: by mapping all of its UI concepts directly to basic constructs and concepts in Elisp, it becomes very easy to globally introduce features for specific kinds of files or circumstances, making Emacs something like a text-based and much more structuredly programmable form of Excel. This presumes that you are going to spend a lot of time customising your environment for personal needs and preferences. Of course, Emacs does do its best to make it easy to stay inside that one environment for everything and anything you may want to do.
Ultimately, neither is superior. They offer different styles, and depending on your proclivities, one or the other will suit your personal needs and way of thinking better. It is always helpful to know both (plus more editors), of course. But you aren’t going to be appreciably more productive this way or that.