I think this is a personal choice and a balance between the look that you like and the amount of effort that you want to put into it. Everyone is different but I'll share my thought process, not that its the right answer but just to give you an idea of what I weighed and how I balanced it out.
Phase 1: coatings. I started with products that I'd classify as protective coatings. These are a bit finicky to apply. youll have to tape off areas, youll need thinner, good brushes, a good weather window, and time.
- Varnish is beautiful and deep. I think that Varnish is by far the most beautiful finish. But I found that it required a lot of upkeep. It's fairly soft and once damaged it will bubble and flake. you sand and recoat to repair.
- Cetol. much tougher than varnish. Its no easier to apply than varnish but you use fewer layers. it easily lasts 2 seasons. Its best to sand it down before recoating (same as varnish). repairs are similar to varnish too. But Cetol looks (to my eyes) pasticy and dull. you can buff it out but it will never be as beautiful or as "deep" as varnish.
phase 2: bare teak. after years of phase 1 I was tired! I saw a few boats with bare teak and I decided to try it. I sanded off the cetol and went bare for 2 years.
Note that sanding off cetl gives you a real appreciation of how tough that coating is!
I just did not like the look of bare teak. To me it looked shabby. the "silver" grey is not awful really but just not to my taste. Worse, the grain began to raise and felt rough. then dirt collects in the low spots and looked even more shabby. I hear that folks maintain bare teak with salt water rinses. I assure you that my teak was frequently rinsed with salt water. but in the end this look just did not work for me.
phase 3: uv stabilized oil. Semco.
- I decided to try Semco an oil. I heard that straight teak oil will oxidize and turn dark, but Semco is UV stabilized and does not turn dark. Its easy to apply, a brush and/or rag. spills wipe up off of fiberglass easily. It is *not* glossy, its a matte finish. it is not as beautiful as a well done varnish job. But it's quite nice and to my eyes much nicer looking than Cetol. And as it ages and wears it simply fades away. it does not go thorugh that awful chipping and flaking stage like Varnish and cetol will.
the high wear areas (handrails, toe rail where I step to enter and exit the boat) will need to be re-applied once or twice in a season. but this is literally a 10 minute job. I'll usually do it while underway when I'm bored waiting for the winds to fill in again.
To me, the beauty scale is:
Varnish is a 10
Semco is an 8 (maybe a 9)
fading semco 7.5
bare teak a 5
chipped flaking varnish a 3
chipped flaking cetol 1