I'm a LINE-X spray-on truck bedliner dealer. Our product is a blend of polyurethane and polyurea. A few points to make:
1. Polyester urethanes are more durable than acrylic urethanes.
2. There are two-part urethanes (polyol resin mixed with a isocyanate (a hardener) and there are one-part urethanes (also called solvent based urethanes) which is urethane suspended in a solvent. Long story short, two-part urethanes are typically harder and more durable than one-part urethanes.
3. There are aromatic urethanes and aliphatic urethanes (depends on the position of the hydrocarbon chains). Aliphatic urethanes are more UV resistant but usually are more expensive.