He was very much in favor of modeless design, which emacs is much closer to than vi is. My argument was that emacs still has modes, operationally. You can make it a debugger, a mail reader, or a text editor by invoking code that puts it in that "mode." So the discussion quickly becomes what is meant by 'mode' and how are operational modes different than semantic modes which are different than presentation modes. If you haven't guessed it was pretty memorable for me, it helped me see some insights into the difference between design and engineering.

I'm not sure that debate was really important since it's clear that his real answer was 'none of the above'.

I'm guessing Emacs, because vi has modes and he was not a fan of modes.