acrylic tung oil which will show surface wear over time in high traffic areas, it can be rejuvenated with application of surface waxes and can be sanded and resurfaced. Harder surfaces will have a higher gloss level. Another option is to use a penetrating oil which has no surface film at all so does not show
tradtional oil based marine varnishes work great but are a lot of work! If your okay with some aging/weather showing go with the pentrating oil finishes. Dalys finishes in Seattle has many options. Good luck!