"Best" really depends on what you use for primer and a clear coat. Its pretty much a system that works together. If there are no adhesion issues, you'll have a longer lasting finish. That being said, I know a lot of painters are using Createx paints (water based). Check the Bear Air and Dixie Art sites for this stuff. Regular colors, florecents, pearl colors, etc. I know others who use taxidermy paints. Quick and easy paint jobs can be done with spray cans. Rustoleum and Krylon are two favorites. Pick one brand and stick with it to avoid compatibility issues.

"Gelcoats", there are a number of products that can be used as a final clear coat over the paint. Easiest to use/obtain is Devcon 2 ton 30 minute epoxy (paint area at Walmart, make sure its the 30 minute). Mix some up and then apply with an acid brush. Hang the plug by the nose, flip and hang by the tail after 10 minutes, fish the next day. Plenty of other epoxies, urethanes, polyurethanes, etc out there that will also work. Probably have to try a few things to see what works best for you.

Andrew