Which is Better, Epoxy or Polyurethane Resins?

The answer to this question is completely dependant on the application.  In some applications, epoxy resin and polyurethane are interchangeable.  You must look at the benefits of each of the materials in relation to the environment to which the final product will be subjected.  Also, there are different requirements for handling and processing of the materials.

In general, epoxy resins will have better chemical resistance, higher temperature resistance, and good adhesion to many substrates.  In general, polyurethanes have lower exotherms, cure quicker, and are better in applications where the product is subjected to wide temperature variation (i.e. -40C to 125C), especially low temperatures.  Properties of materials will vary greatly due to the vast array of possible formulations, so it is best to investigate all applicable requirements before a product is selected and tested.