Well I got both liners so i'll input a little.
My '05 Silverado 2500HD 6'5 bed had a Rhino liner installed by the dealer I got it from in April 2007. I used the hell out of it and threw quite a bit at it, after the 6th month I noticed how it look much more gray than it did when I first got it when it was black. But not a nick or cut in it anywhere.
My F150 has a Line-X liner in it and it appears that its been there for quite some time, and its still black
None the less both liners are great, Line-X is better for those who want a tough & nice looking liner, Rhino is for those that may not mind a little gray ( it'll match the bed rail caps though! ) and possibly have a tonneau. $350 for the Rhino is a great deal though. Just make sure they dont overspray your bed bolts. My Chevys bed is completley covered, so there pretty much no getting that bed off..