clearly vim, or some type of vi
the reason i say this is you know it will be installed. if i log into a shell account, it's not likely to have emacs on it, but you know vi will be there.
i used to be a real emacs advocate but i have to say for a text editor, vim edits text. it's a steep curve to start with, but so is emacs.
having said that, for beginners, pico and nano are great and so is jmacs and jpico