What are you looking to accomplish? Are you wanting to make precision, pinpoint shots at 150 yds or are you just going to be plinking at that distance?
If it were me, and I weren't making a lot of 100+yd shots, I would go with a 1-8ish power scope so I would have the best of both worlds. Medium magnification for the longer range shots and the ability to dial it down to 1 power to make fast, close shots. Beyond that, I would figure out a price range and pick a few scopes in that range to compare side by side.
MY opinion: After trying various power scopes on AR's, I like the 2-7x or 2-8x ones, although a 1-4x would do nicely for your purposes. Either will be smaller than the typical 3-9x and look better on an AR in MY opinion. Quite frankly, I'd look at Sawman's ad selling like new Leupold matte finish variables. Matter of fact, I took my own advice and bought one of his 2-7x ones. Indeed, it was as-new in the box and a savings over buying a brand new one. The 1-6x and 1-8x are fairly new to the field and will cost you more, but would be good choice too if money is not an issue. If you contact Sawman, tell him "Mr. Blackout" referred you.