Quick primer from being in the boat repair business for 15 years.
I'm sure one of the guys with more technical knowledge will point out where I'm wrong.
For making new parts polyester is fine. Polyester has terrible secondary bonding characteristics, so not so good for repairs.
Vinylester is a polyester modified with epoxy molecules. Has excellent secondary bond characteristics, and can be used to make parts, but the benefits are negligible over polyester. shrinks less than polyester, so that might be a plus in part making. Has about a 500 PSI tensile strength.
Epoxy is very strong and completely waterproof. Polyester not so much, Vinylester is somewhat more waterproof than PE but still not completely.
Epoxy can have about a 2000 psi tensile strength. Strong stuff. And expensive!