I have not had Line-x but it does seem more popular these days. Why do you say it is superior to Rhino? Additional info would be helpful. Thanks
Rhino is soft and rubbery. It is much more prone to grip whatever you've got in the bed of your truck, particularly if it's heavy. Because of this it is more prone to rib/tear damage.
Line-X isn't just one coating. They have several, some of which are used by the military for anti-spawl purposes on armor. The coating they use on truck beds has a harder surface than Rhino. That makes it easier to slide heavy objects while greatly resisting damage.
Think about how you use your truck and how you use your back when you load and unload. Do you climb up into the truck bed, position the load just so, and then put it down? Or do you toss it in there and slide it into position?
Having used both products, I think it's an easy choice.