16" or 14.5 + pinned muzzle device
Is the benefit of 14.5" over 16" barrel length so much to make it worth it to SBR a lower or deal with the pain that comes along with pinned/welded muzzle device? What real benefit does the slightly shorter length give you? I don't have experience actually fighting inside structures, but my gut feeling is that if I were going to be fighting in a predominantly urban area, I'd grab my 11.5 on either an SBR, a pistol lower, or a machine gun lower, depending what I had on-hand.
16" or 14.5 + pinned muzzle device
As others have said, your choice of muzzle device is part of the equation. Because I use dead air devices, I can put the flash hider on a 14” Ballistic Advantage barrel to make up the difference (I have a 556 and 308 version). While a 16” with an A2 birdcage, as justin_247 mentioned, is .7” longer, my sandman K won’t work with that. But with the shorter barrel, I save 2” in length with the shorter barrel making it one of the shortest suppressed AR rifles I can take across state lines without paperwork (19” barrel length total with can). That is, with a can that is removable.
But you have to figure out what you want.