Alienx,
As you can see, there's a wide range of optics we're mounting on top of our AR's. It helps to think about how you will be using your gun. Will you be punching paper, long range hunting, short range hunting, etc.? This process will help you determine which scope will best fit your needs. You may or may not need a lot of magnification. I personally like the option of having more magnification (4-16X at least), but the tradeoff is bulk and extra weight. I hope this helps.