Have used and liked bobro. I have a Sidelok mount for an MRO that I'm a big fan of. They make a scope mount too apparently that I'd check out if I was in the market.
Im a huge fan of american defense...LaRue ia good to.
It really depend on the quality of your optic and ar, atleast when it comes to justifying the cost.
Assuming you literally mean for a scope, not a red dot, I liked the Burris AR-PEPR mount that I used to have. It's a solid one piece quick release mount. Next time I scope an AR I'll probably buy another one.
Here's an Amazon link. Mine came with two sets of top rings, with and without a picatinny rail for mounting a small red dot like a Burris FastFire etc.