Wow, I'm surprised about so many votes in favor of the PTR. They're excellent/classic Battle Rifles (tm), but the Scout is a modern design. The16" versus 18" difference is in the noise (and the 16" should be more accurate), the PTR's are not known for their accuracy regardless, they can also be rough on brass, and they are pretty heavy.
I really like them both, but I prefer the Scout. For me, that is the best rifle in terms of price/performance that has hit the market in years. Excellent at almost everything - though not the best at anything.