I have had a few scopes on my ARs, but currently I'm running a Bushnell 4200 2.5-10x50 on my 6x45, a 1.75-6x32 VX3 on my 7.62x39, a 1.5-5x20 VX3 on my BCM Mid-Length and a 3-9x40 VX1 on a heavy barrel 5.56.
The two VX3s are my favorites on the AR because they are smaller and don't throw off the balance as much as the heavier scopes, also their profile is just a bit lower than the others which is helpful with the higher mounting systems found on ARs.
Three of those are in cantilever mounts, my favorite being the DNZ Freedom Reaper. I have the Nikon P223 mount but it's not nearly as well finished or thought out as the DNZ.
The other is in a set of Burris Extreme X-High rings, which work, but are bulky and heavy and frankly very ugly.
The lower powered and lighter Leupolds would be my choice simply because they don't effect the balance as much as a heavier scope will.
