Personally, I'd run 3 wire up to it, then if you decide to use a coolant pump (etc) at a later date, at least you'll have the 120 there as an option.
For that matter, make sure you don't have any relays or contactors that use 120 already.
Rehashing the plug topic... If you haven't already got one... Look at range plugs. They're quite often very cheap (volume sales!), and you can get a plug with a pigtail, and a socket in a combo pack for less than the cost of just an outlet sometimes.
Other bonus is that the plugs usually got a 90* straight down cable to save space.