My goto bare basic scopers are the Vortex strike eagle 1-6x24 if I plan to use it within about 300 yards, and the Diamondback tactical 4-16x44 if I want to shoot from 100 to around 800. Both are in your price range and are decent for that, but just a couple hundred more gets you into the PST2 1-6 and Venom 5-25, which are far better glass and far more capable. They are well worth the cost, the PST2 despite the same magnification is clear enough to make hits confidently a couple hundred yards further than the strike eagle, same with the Venom being a solid upgrade over the DT.
The main thing I like about the Diamondback tactical is that it has a good image and FFP reticle in a relatively compact scope and a really useable magnification range with 30mm body. The 5-25 Venom is a 34mm tube, but the image looks incredible, especially at higher magnification. The 1-8 SE and 6-24 DT aren't worth the $50-100 premium, with the same glass quality the top 2x or 8x respectively isn't all that useable, and starts to loose contrast and has more distortion, would rather spend the money on the better series of scopes. Of course for mounts, I like a QD on ARs, American defense is awesome for the money, and they make one for most any build.
I put the Vortex 1-6x24 Strike Eagle on my Sig 716 and have been happy with it. Really only been out to 200 yds. though. On sale today at DVOR.com for $249.
I know the description says the reticle "subtends for 5.56". I bought it for another build and put it on my 716 "temporarily" and it's still there if that says anything.