2 part international of some sort I would think. I came across a dark blue fisher that had been poorly painted and I ended up using Farecla G3 and removing the paint layer to get back to the gel again. There is a gel coat paint stripper which worked ok but G3 was just as good with a sponge head at 1500rpm.
It would be better to get the area sprayed as the finish would be better though I have seen one guy who hand painted and it looked like it was sprayed it was so good!!
2 pack polyurethane will definitely give the best results and should last many years with reasonable maintenance. Best results for appearance will come from spraying but it's not a DIY job. Brushing should be just as durable but more difficult to get a good finish as Markdj says although there are some hand painters who are as good as sprayers. I would recommend talking to a few boat painters and ask which brand they use (and why) for the application method you choose.
Unless you really need to do it I would avoid painting the superstructure. As with all paint jobs preparation is crucial and superstructures are very difficult to prepare and mask properly. When painting it will be almost impossible to avoid dust in the paint and every imperfection will be visible.
2 Pack is best by far, but the right conditions and the best of preparation is required. International Paints two pack has come a long way since the 70's and now that they have the Awlgrip know how I believe it to be a superior product for both brushing and spraying but either method is not for the faint hearted!
Single pack can be easier to apply, but not as tough, fender rub can show very quickly, but on the plus side can be touched up quickly and easily and whereas 2pack could last 10?years I have had a single pack paint job last 5 years before a full repaint was required (with the odd touch up)