Welcome! You have come to the right place, hopefully you won't get more confused, but let me try.
What do you want the rifle for? Fooling around at the range? 3-gun competition? Any chance of precision bullseye shooting? The 20" has the advantage of faster velocity, and a longer sight radius. For a range gun (or a hunting gun), it is hard to beat.
The 16" is handier for carry, and can be swung faster for 3-gun type matches. If you plan on mounting a scope, the sight radius thing is irrelevant. The accuracy should be the same, that is not a factor.
I have a 20" A2, and couldn't be happier with it. I don't care about scopes for the moment, so the fixed carry handle is okay. If you plan on using a scope, you might consider an A3 model, since it's handier and more versatile.
The stock is higly subjective, personally I think that the post-ban fake "collapsibles" look wrong, it's purely cosmetic. And most people prefer the feel of the full stock, as you can get a better cheek weld. Another option would be to go for the Ace skeleton stock, it doesn't look nearly as "wrong" as the fixed, extended "collapsible" stock, and still has a certain cool factor.
Just a little more info from you, and we might be able to steer you in the right direction...