The CM 612 PWM and Scythe Mugen 3 were as close as you could get in performance (5-7C better than the 212). When user was in the $50 cooler category, I usually bought whichever was cheaper that day. Based upon that experiences, I'd say Scythe had the better mounting system.
But I have to note that I have had two builds come in with problems in the last cupla months whereby the Memory OK Red LED was On. I traced the problem in both instances to scored motherboard surfaces (interrupting printed circuits) from the standoff screws for Hyper 212 installations. I never had the problem on builds I have done but I added thin textile or plastic washers under the standoffs (these don't come with the kit).