If you want a 2-in-1 that works, International just released a "Polish & Wax" (that's a bottle with both words on, as opposed to two bottles with one word each). After being given a sample, I bought two bottles, as it was the first 2-in-1 that actually worked for me.
The best product to use depends on the state of the gelcoat, not the boat manufacturer or anything else. If the gelcoat is discoloured you need a cleaning product first (or oxalic acid), if it's very chalky (UV damaged), you need a more abrasive polish first.