My personal favorite!! - Samson KM-EVO-1237 Evolution Keymod AR-15 Aluminum 12.37in Rail

Originally purchased one of these handguard rails for a AR I was putting a piston system on, and I was very impressed with the quality and the rock solid sturdiness of the rail, I’ve owned a few different rails including high end ones like Diamondhead but in my humble opinion the Samson KM-EVO-1237 Evolution series of rails puts the others I’ve owned to shame. Don’t think they could be much better. I'm up to my third purchase of these rails as I write this and have had no issues and experienced 0 defects. I highly recommend.