I'm a vi user (or to be more precise: vim user). It's one of the most efficient editors ever created although maybe not one of the most user-friendly ones. However, it has a lot of advantages. For example, it's available on virtually every Unix or Unix-like system. At Comdasys, we have vim on all of our products because it's quite small (if you remove all the data files like syntax and help files) yet very powerful.
I wrote a little quick reference years ago. I should propably make a better one sometime but until then I'm providing my old quick reference here.