The difference in length between a 14.5 with a permanent flash suppressor and a 16" weapon with an A2 suppressor is very, very small. I played around with 14.5s with permanent suppressors, but it got expensive and I couldn't swap out my rails and such. I prefer 14.5 as a barrel length, but get 16" barrels now because I cannot SBR them in my state.
You will not notice a difference in accuracy. At a distance the wind will push the 14.5s bullets a bit more, but if you are a good enough shot to notice the difference you can probably dope the wind well enough it doesn't matter. Compactness.....is pretty much a draw. The difference is not very noticeable. If you put the rail on BEFORE you attach the suppressor, you can use anything. Otherwise look into the SIR and the RAS 2. There are more options than that, but I don't know much about them. For twist...if you are going to shoot ONLY 55gr and 62gr ammunition, 1/9 will serve you well. If you want to use 75 or 77gr ammunition later, get 1/7. There is no downside to 1/7, but 1/9 is limited. I would say just get the 1/7.
All in all, I would say you are best off with a 16" 1/7 barrel, preferably a mid length. 14.5 is nice on an NFA weapon, but it is not worth the extra work on a title 1 (non-NFA) weapon.