The Carbine gas system is fine for 14.5″ barrels, but if you are considering a 16″ barrel, I highly recommend a mid-length gas system.
The mid-length is much better suited for a barrel of this length. Not only is it more inherently reliable (and closer to the original 20″ rifle length gas system that the AR15 was designed for originally), the mid-length system does less wear and tear on the rifle, has an increased sight radius, and produces slightly less recoil than a carbine gas system.
Unfortunately, the mid-length is not as common and easy to get as a carbine length 16″. The bright side is, they are becoming more popular and common, and it just so happens that my favorite AR15 brand is producing them.
Not only are the BCM uppers well priced, they offer milspec quality such as HPT/MP Inspected proper MIL-B-11595E barrel steel chambered in 5.56, M4 feedramps, chrome lining, and a 1/7 twist. In short, you get Colt quality for a lot less $$ and in a variety of different configurations.