If I'm going to be using an AR within the legal limits (16" barrel minimum), I want 16" of barrel, not 11.5" with a 5" tube that only destroys ballistics or similar things. I want an extra 2" of sight radius, etc. I want handguards that take advantage of that. I don't want an extra 2" of pipe sticking out. I also want a heavy barrel. On a 16" gun, that's no big deal as far as weight is concerned, but I'm also used to my FALs.
For me, that meant the only option was really the RRA Elite CAR upper in a mid-length configuration. I also will only buy a flattop - the thing should have been built that way from the get-go.
I also have no need for four sided-rails and most of the other stuff. I do have BUIS with the rail extension and a red dot that's permanently mounted to extension for zero in the event that I actually remove the night vision scope.
Resale hurts you with a A2 only option these days big-time.
Any of the major brands (RRA/Colt/Bushmaster) will deliver quality rifles with good resale value.
Don't get me wrong - for me the AR is a special purpose rifle (light enough to be effective when moving with a night vision scope) only.
But I think I've pretty well outlined my how and why.