Wax. Go with a high tech wax like "Nufinish" and it will help preserve the gel coat nicely (and make it easier to wash).

As far as restoring the shine, I recommend looking at a product called "Vertglas". I used it on my monohull and the outcome was spectacular. I had two people think that the boat was brand new (It's 21 years old). You have to be careful what you clean it with but even that's not a big deal once you get the right stuff.