Skeejunky,
I was looking for the best optic for a new AR15 (but not my first) just a month or so ago. I did a bunch of reading here ar AR15.com and loooke around at gun shops. Locally I could not find much besided outdated stuff. I did see one ACOG (by Trijicon) and they are very good low power scoopes. I found a model that I thought wold be the best for me. Problem was it was $800 and that just would not work out for me. in looking around I settled on the EOTech 511, and now have it on my new rifle, shot it just yesterday.
The EOTch is a hallographic heads up type display somewhat similar to an Aimpoing red dot is use. While it (or the regular Aimpoint) does not provide magnification it does give a precise aiming point and the low parralax error concept (like Aimpoint) is really nice! Paid $284 for my EOTech, some models are a bit less. They mount directly to a flat top upper. I reccomend them!
The OKO sight is around $200. While I have no personal experience they generally find acceptance as the least expensive reliable red dot type sight. Do not forget about mounts, they can add up to $100 to your optic!
There are lots of alternatives, so read up before spending thsat hard earned money.