IME, most of your name-brand drop-in rails are going to offer about the same quality and functionality. I have installed Troy, Midwest Industries and the Daniel Defense EZ-CAR for customers in the recent past, and they all went on easily and locked up pretty tight. I'd give MI the nod for economy and ease of installation, although they are potentially a bit less stable than the others, as the two halves do not screw together and there is no additional tension beyond that provided by the delta ring.
The Daniel Defense Omega rail is a 2-piece drop-in design, but it allows the barrel to free-float; it is AFAIK one of the only such systems out there. Great quality and features and extremely lightweight, but