I hate to lead with the 'it depends' because if doesn't help, even if it's true. It sounds like your friend said 'scope' and not 'red dot'. If it's a scope, for an AR, I don't think you can do much better in price versus performance than the Nikon M223 series. Great glass, reasonable features, good control feel, well adapted to the rifle. And not too bad on the wallet. Yes there are others, but when it comes down to buying an optic, one of my decision points is who has a great history of making great glass. I own Nikon in the mid-range, and a Leica in the (painfully) high end.
If your friend meant 'red dot', the Aim Point is excellent, though you can get good ones (though not as good) for less than half the price of the Aim Point such as the Vortex SPARC. I have two and they are not bad at all. And, in the Aim Point price level, I tend to prefer the EOTech. I know that the AP has much longer battery life, but the EOTech isn't bad really and the 'holographic-like' projection provides a better view for my eyes. Don't pay for the night vision feature in the red-dots since it is unlikely that it will be needed.
GL,
B