[dbiscayne]

I'd vote for epoxy, have used both and it always seems that the accidental drops of epoxy are stuck to whatever they land on better than vinylester, ie you can usually chip a stray drop of vinyester off & it'll come off cleanly, not so with epoxy it usually takes a layer of whatever it landed on with it.
Lots of good scientific data on the web that back up epoxy when fixing or adding to an existing cured structure.