Gotta agree with BP's first impression.
Looks like the small room is the way to go.. as best I can tell... after adjustment for closets etcetera, the smaller room is actually about as big, or bigger.. and doesn't have the masking problems of the slighty "smaller" room.
The standard wisdom is to put your mix desk facing the short wall, so that your listening position is about 40% off the front wall as measured down the long axis of the room.
Though very tight, a room this small, as long as you add early reflection control and some broadband treatment in the corners you can still make yourself a "decent" critical listening environment.
Nonetheless... given the size of the room, I would want to add a sub... unless your monitors have truly superlative LF performance.
Good Luck!
PS: These subs are a pretty darn good bang per $ IMO and add a lot of detail to the average value rig... YMMV
http://www.partsexpress.com/webpage....536&filter=kit