Originally Posted by mtb-chop
.........One other variable is the cables. Old, dirty cables will shift like crap. People have their preferences, but mine are the Avid Flak Jackets - fully sealed with a great compressionless housing. I've had no problems with mud or ghost shifting.
I vote Shimano with a quality set of sealed cables.
Very good point on the cables. I had a problem similar to this a few months ago. Come to find out my relatively new cables had some rust which caused the cable to not be released all the way. I adjusted and adjusted the derailleurs with no results. As soon as I took the cable off the problem was plain as day.