Avid Elixr CR came on my 2010 Stumpjumper and have worked flawlessly for me, but I had Juicy 7's on my old hardtail and they shuddered constantly--it was awful. My friend bought a 2009 Stumpjumper and had a lot of noise/vibration problems at first but they (Specialized) sent him new rear rotors under the warranty and it fixed his problem and they've been perfect. My wife's 2004 had Shimano XT/XTR discs on them and they're still going strong--never made a peep and she absolutely loves them.