Personally, I started out using Emacs because I wasn't a big fan of the "modal" style of vi (insert/command mode). Later on, I started pair programming in shared GNU Screen sessions, in which we ran vim; a pile of "how did you make that change so quickly" questions later, and I ended up switching to vim for the speed of basic text editing tasks, which save more time than I lose by not having as many high-level mode-specific commands.

However, I still use Emacs for LaTeX documents via AUCTeX, because I find it far more powerful for basic editing, with commands to insert directives, environments, \item, etc.