A few more things about epoxy vs. polyester.
Polyester is actually rather nasty too, and in fact is more dangerous than epoxy in that the MEK in it (or some other volatile compound, I forget) is absorbed rather easily by breathing and also through skin. So, if you work with it and start feeling lightheaded or dizzy - don't be surprized
It requires a proper filtering organic respirator and good gloves and sleeves to avoid getting this stuff on your skin. This is one reason many repairmen prefer not to deal with it (confided to me on two separate occasions by two different pro-s).
One more issue which is something to consider - epoxy, while in itself a harder material and better suited for mecanical bonds (think "velcro style" bond), does not have much solvents in it and as such neither penetrates the surface too deeply, nor creates a primary chemical bond with polyester resin. So, when you repair polyester GRP with epoxy - think of it as a big velcro style patch placed on. Since thermal expansion coefficients for epoxy and polyester are different, and the bond is mechanical - it is not impossible for the two compounds to lose their bond over time (since one expands and contracts by a different distance from the other, those little "hooks and loops" can lose their grip). This is one reason, I believe, that I found many failed or very obvious boat deck repairs when made with epoxy. This also may (according to some surveyors) be a reason for "catastrophic failure" of some of those epoxy barrier coat jobs, though being under water I expect them to be less subject to heating and thermal expansion.
So, personally, I prefer polyester resin when repairing decks and superstructure. Epoxy is good for bonding, tabbing - especially wooden parts. It is also easier to use for underwater repairs.
Vinylester is extremely poisonous, more so than polyester, so working with it is probably not for the do-it-yourselfers.