I believe 16 is the shortest one can go without needing to purchase an ATF license or stamp or whatever to own a true short 10 inch barrel. 16 is still short enough and no matter what gun you get it will be heavier than you were expecting.
I went shooting for the first time in years and was surprised how much heavier it felt in my now old and out of shape hands. I like Lewis Machine and Tool but those are pricey.
Armalite is a good brand. Do some pushups :).