My brothers SRS is the 16”, and fairly stock(only mod is fast hop, hop rubber and Nub- highly recommend you do this ASAP as it allows the gun to lift much higher ammo)
I will always go for the shortest version. It’s lighter, easier to wield and as @sonofsammo said easier to hide. Plus you save money buying it.
The difference between my brothers and my team mates SRS in price is £100s but range wise it’s only 15-20M... The real difference between them is noise, there are many cheap mods to make it super quiet. If you have had a read of my comparison and earlier posts about the SRS, you’ll know exactly what I’m talking about.