One of the higher end ones, larue, noveske, LWRC are the other high end ARs. Honestly a lower is a lower its the barrels in those higher end rifles that make them higher end rifles. Build a lower and get spikes or one of those uppers and you'll be all set.
I have a Spikes 16" midlength upper with one of their FF rails. I continuously abuse the hell out of it, and its still more accurate than I am, and as reliable as anyone can ask for.