If you get a Colt AR, make sure the pins are all milspec (hammer, trigger, retaining pins). Depends on date of manufacture. You want milspec pins so you can interchange with common parts.
My preference for a factory Colt is the 6721 with a heavy barrel. Here is a link to a thread Colt 6920 vs 6721 - M4Carbine.net Forums
There are also piston type AR's (vs. original direct impingement). For your purposes, a DI rifle is fine. I have always had DI rifles but getting a piston PWS soon. I drool over the HK MR556 but it's a little too rich for my blood.
But get one soon (or two ). If there is a re-election in November, there will probably be another shortage of ARs and ammo (and inflated prices). I was glad I already had a couple (and ammo) after seeing what was going on a couple of years ago. There was a period where not much was available or expensive. It's a good time right now but not sure what will happen with demand when November gets closer.