Top tube length is arguably the more critical dimension here - there's about a 1" difference between the two frames you're looking at. Be aware that you may need to be a little more stretched out / less upright than you might be used to (unless you have serious road biking roots)
Loosely speaking I'd lean towards the larger frame for better climbing ability and long distances, smaller frame more for jumping and DHish sort of stuff (with the caveat that this is NOT a DJ or DH bike). So if you really are in between sizes then it kinda depends on what sort of riding you see yourself mostly doing.
The only way to be sure is to test ride bikes of similar dimensions and see which fits you better.