I've got an LMT Piston. I can only speak for my rifle. I have had no issues and really like the options that come with it. Others might think those options are negatives, but I try to look on the positive side on most things!!!
That being said, there are those here and on other sites that have LMTs, LWRCIs, and POFs as 'factory' units and are very happy with these. Have you read about the ADC here: http://www.m4carbine.net/showthread.php?t=15229
Which ever you choose, please do your research first. LMT, LWRCI, and POF are all within a couple hundred dollars of each other which shouldn't influence your decision. Whichever you decide, make sure your bolt carrier is a one piece design or at least have the piece that the rod pushes on milled into the carrier.
Good luck and happy shooting!!