I guess it depends on what you want it for. If you want something "old School" I'd go with a Colt. You'll pay more.....but it's a Colt.

If you want something new to hunt and plink with then there are a lot of different manufacturers that make good AR's. As mentioned I'd go with a flat top because you will have a lot of options as far as sights go.

Me, I have both...but I prefer "old School"