It really isn't that hard. Do yourself a simple little test.
Make 2 decent sized signs. Exact same design - ideally something with heavy color saturation.
Print one on cheap calendared stuff, and one on a good cast vinyl. Now, laminate HALF of each one. Apply them to the same substrate type (I'd suggest polymetal, although you could go with PVC).
Now, go put both signs up on your roof, facing upwards, for the rest of the summer.
You now have a VISUAL display of what the wrong materials will do to a sign.