Absolutely no polymer lowers. They aren't proven yet and have alot of development to go.
Great lowers include: Noveske, Larue, Colt, BCM, S&W, LMT, Daniel Defense, and maybe Knights Armament. Find any of those at $400 or less today and buy without hesitation IMO.
But in all honesty, a lower is a lower. As long as its within spec, they all will work.
"You'll Never Walk Alone"
"Psycho Murican" -- beeemerdude of Canada