my buddy had an X7 on his bike and the shifting sucked, and was way too loud in anything but the middle few gears. I swapped in an old xt derailleur I had laying around and he has been raving about it ever since. Shimano is still tops on front mechs
Have to agree with other posters, Shimano XT is probably best bang for the buck in front derailleurs. I have XTR on a couple of bikes, and while they do seem to shift a bit better unless you manage to snag XTR at mega-closeout pricing (which I did) they are not worth paying the 2-3 times what XT goes for.