Emacs, which to use?

There seem to be the following versions: emacs23, emacs23-nox, e3, emacs23-lucid, and jove, as choices to download. Where can I find out what the differences are?

The short answer is that you almost certainly want emacs23: it's the full version of Emacs 23 with graphical support.

emacs23-nox is the same, but without any graphical support. If you're installing Emacs onto a server or other environment that lacks an X window system, you should fetch this version instead. (Note that emacs23 works just fine on the terminal, so the only reason to prefer emacs23-nox to emacs23 is if you don't want to drag in the dependencies.)

e3 and jove are not Emacs; they're lightweight editors that have Emacs modes to them.

emacs23-lucid is XEmacs, which used to be called "Lucid Emacs".