Welcome to the forum, Setter!
I'd say go with the 170's. I have mine in a room that is approx. 13' x 18' and they do great. depending on budget and future upgrade plans, you could pick up a Hsu sub with the 170's and probably get a package deal from Ascend.
When you eventually upgrade to 5.1/7.1, you can pick up a 340 center and either add a pair of HTM-200's for surrounds, or add another pair of 170's for that duty, or move the 170's you started with to surround duty and add 340 mains. Lots of possibilities.
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables