Asking what varnish is best is close to asking what is the best religion. Let me preface by saying I haven't applied varnish to epoxy but I have used different types on the wood on my sailboats. I used Schooner96 for years and found it was not only great UV protector but gave a very nice gloss; last year, at the suggestion of a friend, I tried Epifanes and have never gotten such a deep gloss before. It was more difficult to use in that it seemed a lot thicker and it took me awhile to learn how to thin properly. Captains varnish is used in the northern climes because it dries better in the colder weather ( so I am told by a Maine boatbuilder)but I found it to be a little thinner and therefore required more coats than either Schooner or Epifanes . All in all, if you haven't varnished before I would recommend Schooner 96 for a balance between a very good finish and ease of use.
Alex Warren