Everyone will have their own preference so you are going to get a lot of answers. I like varnish outside the cabin but not inside. I used to use oil but years ago met a guy who worked on super yachts for a living. He told me that oil attracts too much dirt and pointed me toward Liquid Gold. I've been using it since and am just finishing our new 2017 R25. I do a section at a time and because the wood here has never been treated at all I brush it on as I'm leaving the boat and let it soak in for a few days. Give it a quick rub when you get back to make sure there's no excess.
As I said, everyone will have their "like". Why not try a couple of ideas in hidden areas and find yours before you do the whole thing?