ORIGINAL: Louis9624
One thing to consider is vinylester resin has viscosity much thinner that epoxy. This may not be an issue, buit if you are covering balsa wood, I think it will be absorbed by the wood, making for a heavier part. This may or may not be bad, (more strength for the wood). Vinylester is usually a little higher strength, but don't be fooled, vinylester is a little more brittle.
I always seal the balsa regardless of the resin. There are many high quality epoxy resins that have near the same viscosity as vinyl ester.
Epoxy typically has a higher tensile, compression, and interlaminar strength than vinyl ester.