I have a Brooks B-17 Narrow on my touring bike and on my 'slop' bike (a Stumpjumper hardtail), a Brooks Pro on my commuting bike, a Selle Italia Flite on my Moots and on my Stumpjumper FSR.
I can definately tell a difference between the Brooks saddles with the B-17N being just a little more comfortable than the Pro. And the plastic saddles are definately less comfortable but they work better on a mountain bike then the Brooks...can't get a Brooks back far enough.