Resins are like boats. They're all a compromise. Dave Gerr explains it better than I, but some things to consider:
- Secondary bond strength (do it stick to the substrate?)
- Physical properties (tensile strength/elongation, compressive strength, etc)
- Ease of use (learning curve for correct mixing/catalyzing)
- Cure time
- Cost $$
I've used polyester and epoxy, but not vinylester. I buy my resins from US Composites, and their vinylester isn't much cheaper than their epoxy. My rule of thumb is to use epoxy where strength or secondary bond is the primary concern, and polyester for fabricated parts. If I were doing a transom, I'd use epoxy. Some would say it's overkill. They may be right, but to me, it's worth the extra $15/gal for the superior bond strength.
Dave