Sig, I want the most effective suppressor and don't have a plan to use on other calibers. Right now I am sitting with a 16in barrel.
Go with ANY brand you feel comfortable with that has decent reviews that is both the shortest and lightest suppressor rated for that caliber (and not larger).
The next pain in the butt question I forgot to ask is if you want a direct thread mount or a quick detach mount? If it's only 16" 5.56, direct thread may be a good option. With a QD mount, I can switch cans on and off barrels pretty quick, even if the can is rated for a larger caliber (putting a smaller can on a larger barrel that would would with a QD mount would end up putting a bigger exit hole in your suppressor which isn't good LOL).
Thing is, if you want the most effective suppressor on a 16" AR barrel, to me the extra size and weight of the "best" suppressor you can find really isn't worth it price wise over a dedicated smaller and lighter can.
When I have people shoot a 6" can weighing 13 ozs vs a 9" can weighing 24 ozs without hearing protection, it's kind of a toss up to what suprpessor people think is actually quieter. They are both kind of loud with the sonic crack.
That said, my first can was a .30 caliber can which I can use off my .300 win mag along with my 5.56 rifles. It's nice, but bigger and heavier on a 10" AR. My last dedicated "rifle" can was the smallest and lightest, which I personally like the most on the 5.56 which I can still use on a 10" AR.
My one friend. While this picture was taken, he didn't own a suppressor. After he shot more than a couple, he absolutely had to get one (or two). Kind of funny, he called his wife and said "hey, we've got to get a couple!".
He got a 30 caliber can than he can use on his .308 and his AR's, and got a .45 can (same as in the pic) for .45, 9MM and .22LR (if he wants to use it that way). $1,200 covered his two tax stamps and 2 suppressors. That's actually a good deal for buying them.