I use Emacs. … except for mailing with mutt. In that case (typically in a Putty terminal) I use vi. Okay, sometimes I have emacs running in that putty session and read the mails with ansi-term mode and mutt. In this case my editor is emacsclient. Though I am still curious what will happen if vi opens in an ansi-term buffer. The 5 things that keep me with emacs are:

I never got into Mail with Gnus. And also the other MUAs (Mew, VM, Wanderlust) didn’t suite me, so I just stick with mutt (“the one that sucks less”).

Welcome to the wiki. – DrewAdams