Both models look fairly similar in construction and components. Best thing to do it try them out for a test ride and see if you prefer the feel of one over the other. The returned Cannondale sounds like a good deal, assuming it was not returned for being defective. I also noticed with an image search that the Cannondale has a guard around the chainrings, which might be convenient on a commuter bike.

I'm also 5"7", here's my similar bike, if it helps give you any idea what size range you are looking at:

Port Bolivar by Yo Spiff, on Flickr