After having several boats with far too much exterior teak and located in South Florida for 20+ years, this was the solution I chose for my last boat, the Cape Dory 28:

1. Seal all exterior teak (other than teak decks) with 2-part epoxy resin. I used 1:1 resin, but 2:1 would brush out better.

2. All teak that was indirectly exposed (i.e., the windshield frame was solid teak with a "navy" top attached, so the "inside" surface was never in direct sunlight) I applied a high quality marine varnish to protect the epoxy. Use a "spar" varnish with a high UV protection content. It required a slight amount of touch-up after 2 years.

3. All teak than was directly exposed to the sun, I painted over the cured epoxy. I chose to paint because it was easier to touch-up than varnish and the brown color looked great. It needed some touch-up after about 1 year.