I would give vim a miss - particularly if they'll be hacking xmonad.hs in the near future - emacs has much better Haskell support (I believe). The same is true for dozens of functional languages. I can't be doing with the confusion of multiple editors, so emacs wins for me purely based on the languages it supports.

I wish I became familiar with emacs a lot earlier. It took me ages to transition from using IDEs because of the steep learning curve.

Oh, and I wish I grew up with a Dvorak keyboard. I was forced to learn it after getting RSI about 8 years ago - but I'm better for it now.