IMO go w/Line-X if it is within your budget. A buddy of mine owned a franchise and there are some differences between the two products, so depending on what your need/use of a liner is you will want to consider both. For example if you need the all out protection similar to what a plastic drop in liner provides you want the Line-X, however if you are planning to carry a lot of things and don't want them to slide around, then the Rhino lining would be a better choice.

When my buddy had the shop he removed several Rhino linings(at $80/hr) to replace them with Line-X, because the customers found that the Rhino didn't match their need. As a display he had the local Rhino shop shoot 1/2 of a tailgate and shot the other 1/2 w/Line-X. While it helped sell Line-X, it also helped the customer decide the type of liner they needed. If neither shop has a display similar, take in a piece of sheet metal, cardboard, ply-wood, etc and have each shop shoot 1/2 of it, they should do it for free, seeing at what you would be spending on the liner. This way you could run some tests on each and see for yourself which liner will work best for you.