Re: vortex scopes
Depending on the type of shooting you're doing, as well as your budget, I'd recommend both the Viper PST and Razor products. Razor glass is cleeeeean, like Cobra mentioned above, but that's the extent of my familiarity with it is looking through it.
I have the Viper PST 1-4x MOA (second focal plane) on my 18" AR and it's great out to 600 yds on steel so far (400 on paper). I like the illumination in low light, and the zoom ring gives you multipliers at different magnifications IF you want to do any ranging using the MOA reticle. The FFP models are a little pricier but let you range with the reticle at any magnification.
Just use the Hide Search feature down and to the right of your screen and you'll find tons of info on these optics; pro's, con's, prices, features, etc. Good luck!