When I was in college, my first class that used computers, a numerical methods class using FORTRAN77, told me to use vi as the editor. So I learned how to use vi for basic editing.

When I was in graduate school, the first computers I got set up with in my department were a VMS cluster. vi was not available, and everyone used emacs. So I started using emacs. This was emacs 18, emacs 19 and later had yet to be released. Pretty soon, I found vi-mode, and then viper-mode, which I used for a few months. I started using a bunch of features that vi didn't have, such as splitting the window. Eventually, as it was horribly slow, I totally abandoned viper-mode and just used the straight emacs bindings. So, that's how I came to be an emacs user.

However, to this day, if I want to edit a file from the shell, I'll start up vi, because vi is quicker to type than emacs, and vi (or elvis or vim or whatever the vi that was there was) starts up much more quickly.

But I'll always have an emacs window around. One emacs feature that I overuse is hippie-expand. I have it bound to M-TAB, or, as I type it, C-M-i (or on keyboards without a meta key, C-[ C-i). I suppose identifier completion is a feature of IDEs, which I hate using. But I've been using hippie-expand for over 15 years.