Well, personally there are somethings that I look for in the optics I put on my AR's. Primarily this comes from really learning how to shoot accurately on a bolt gun.
1. Fixed magnification. I haven't really had a need to get more than 10x, tried a variable once, just didn't really see why I needed it after trying it against my 10x. That is personal preference all of the way. What I will say is that I can put rather nice little 30 round groups (sub 5") at 300 meters with a 20" AR and a Burris 3200 Elite 10x mildot scope. Is that great or grand by professional or competition standards, nah.. but it does equal one very dead object at 300m.
2. Look for target knobs, not for something that requires you remove a cap (which will invariably get lost) and dig out a coin to adjust. Quick windage and elevation adjustments are important to me personally.
3. Learn to use and love the MilDot reticle. By far the easiest sighting reticle I've tried in the decade plus that I've been shooting at any sort of real distance. It also allows you to not have to crank on knobs in quick shot, moving target or variable targets at variable ranges if you know how to use it for hold overs.
4. Give serious consideration to Bell size and tube diameter. 30mm tubes will be brighter and more crisp in general. But 1" tubes are pretty good for most folks. I've got a few of each and the 30" tubes make for brighter optics over all.
5. Consider actual eye relief and parallax. Again with variable optics these two points change as you adjust the magnification. This means you're changing your cheek weld and more than likely your grip and the stock placement. That means that you can't train to use the same spot on the stock and grip every single time. That means you'll lose time lining up behind the scope... can be a show stopper in more than one way.
So no you don't have to spend $2500 on a S&B or USO scope.. though if you have that kind of spare cash, they are absolutely amazing optics.. but you can stick in the sub $400 range and get some quality optics that will more than do the job at hand.
Those are my humble observations and preferences. Take it and them for what it might be worth.
