There is no definitive answer. Everything is opinion orientated for the most part.
I have used Meguiars Marine/RV Cleaner Wax. It polishes (removes the streaks) and seals. Don't know if its the best but it seems to work pretty well.
http://www.autogeek.net/boat-cleaner-wax.html
I have been told by a pro in the paint/boat care business that the best wax they have come across is made by Camco, called Armada T Wax (True Wax)
http://www.shipstore.com.../HTML/CAC/CAC40966.html
As stated in Meguiars FAQ, the proper way is to polish first to clean the paint of oxidation etc and then seal with a wax. A real polish does NOT seal even though several manufacturers claim their polish does.
A good polish I have found is Turtle Wax F21 (formerly, 2001)
http://automotive.hardwa...-car-polish-144246.aspx
-Karl
1986, 32' Sedan, twin 360ci, 275hp Chrysler's w/ K&N flame arrestors