Just refinished wood grained fiberglass exterior door & would like to know if spar varnish or polyurethane should be used as the finishing coat. What brand is the “best”?

I have a white siding house with black shutters, grey/black roof and red and white brick trimming the bottom of the covered front porch. I want to paint my front door black, it is mostly lead glass but I have no idea what kind of paint or what tools to