Willy:
In my opinon -fully sythentic is the only way to go. I personnally like Mothers FX. Very easy to apply and wipe off, but still stands up well to the weather and Wal-Mart has it for $8.00 a bottle in my area.
Make sure you apply in thin coats not heavy. Gelcoat has small peaks and valleys which need to be filled slowly making a smooth surface. Don't try to golb the stuff on - multiple thin coats and slowly build up the surface. (You'll know when the surface is build up becasue it becomes easier to wax and wipe off over time). Here a picture of a 26 year old boat that's never- ever been stored in side! If you look close at the rod holder up front you can see the reflection of the rod off the gel coat. Be careful though. It' s sticker than you how what when it gets wet!
I have used Poliglow lbut in the long run I wasn't happy with it. It to like wax will wear off and mine began to turn yellow with age. If your gelcoat in good conditon, a full sythenic wax is all that's needed.
Kamikaze