I've got an Armalite and a Rock River. I like the Armalite 'cause it sits slightly lower than the Rock River (doesn't look so strange with a 40mm objective. The Rock River is made high so that back-up iron sights will fit under them. Rock River was $60, Armalite was $80-$90.
Here's a nice comparison of several one-piece mounts:
http://www.maxicon.com/guns/optics/one_piece/ar15_onepiece_mounts.htm
