I've tried both. Poly and Captains work equally well over epoxy as far as I could tell. The problem with epoxy is that it will peal away from edges if any water can get in there, so it works best when the part can be encapsulated with epoxy to seal it. Also any chip or ding in the surface will quickly cause the epoxy to lift. Removing epoxy is also very difficult. I eventually removed all of it and just went back to Captains. There is no holy grail of bright-work finish, and over the years I have tried most of them. The latest fad seems to be Honey Teak or the new Cetol, neither look as good as varnish but seem to last longer. Whatever you use you will have to keep at it.
Why not just let it go silver/gray?