I've delt with this quite a bit when I was the quasi "fleet manager" for our company. I've used plastic liners, rubber matts, plywood and spray on.
Plastic liners will hurt you because they are just too slick. Rubber mats are pretty good, but will bunch up and allow your cargo to slide if you have to make a sudden stop. Plywood is very good if you carry heavy cargo, but it will leave the bed of your truck in pretty rough looking condition after a few years. Spray on liners are probably the best for appearance, durability, slip resistance and clean up. You'll probably get at least half your money back for a spray on liner when you go to sell your truck. JMHO.
