Preferably an IDE. Integrated support for Subversion/Git is a big plus as we are a group of 6 people working.
Vim/Emacs is not that pop
RubyMine 4.0 (Early Access, US$59 w/free upgrade to 4.0 release) has VCS support (git et al.), debugging, node support, like a full-blown IDE. It also has CoffeeScript support, though it falls down (as I recall) on debugging --- you end up back in JavaScript land --- which is where I'm doing most of my work now.
I'm using it right now with node, express, and JavaScript (mostly) and CoffeeScript (little experiments).
I assume RubyMine is a superset of WebStorm (same company). However, for $20 extra, you get ruby + JavaScript IDE, so I would suggest going with RubyMine if you have any inkling of doing ruby or rails in the near future.