Quoted:
I wouldn't have a 14.5 that wasn't an SBR. If you ever want to change rails, and you will, you're hosed.
A perma flash muzzle device not stop you from changing rails. Your selection goes down, but there are many out there that use the standard barrel nut. You're limited as to gas blocks for the most part, but a cut down FSB is the best gas block available, so no worries there.
Only downside to a 14.5 is that you cannot change muzzle devices and you lose some velocity. Ultimately, 99.9% of the time you won't notice the loss in velocity and that is assuming you are in the .00001% of people int his world who use their AR15 against something trying to kill them.
A lot of the fuss of a 14.5 comes with the lesser velocity. When shooting FMJ velocity is very important. When you're shooting TSX or whatever bullet you choose for pigs velocity is not as important. Still important, just not as critical as the golden "fragmentation" velocities with FMJ, assuming you subscribe to all that jazz.
Either way its a matter of time before you have both