Yeah - I definitely would not use polyester; it does not stick to old work well, shrinks, and blisters. Depending on what I am doing, I use either Raka epoxy or vinyl ester. Vinyl ester has about a 3-6 month shelf life but the MEKP catalyst is more like 2 months. Epoxy is very long - I have been told a few years (thats good for me
). Both VE and Epoxy have very low water permeability and shrink lots less than polyester. Gelcoat will stick to VE but not as well to epoxy. If it is going to be painted with an epoxy or remain bare, I mostly use epoxy. In higher humidity epoxy will blush but VE does not have that problem. I usually use peel ply on epoxy to eliminate that problem. For me epoxy is a little easier to use since you just pick the right hardener and go with it rather than trying to figure out how much catalyst to use for the expected temps. I used epoxy for my transom recore and other 'hidden' work, but used VE for my new decks since I am using a VE based gelcoat on those. Short version - they all have pros/cons; kinda depends on exactly what you are doing. And avoid poly for anything except mold making.