I'm one of those who watches the roof, and fiberglass is far better than the membrane types, as it means the seams can be located at places that the wind isn't forcing water into the vehicle.
Ron Dittmar has an excellent explanation for what to look and what not to get, and this can save you tens of thousands in water damage.
Were I looking for a class C right now, I'd see about a FR Solera, either a 24R (gives one a sorta-walkaround queen bed in the back, as well as 27 feet of length in a 24 foot package), or a 24S, which everything works well, even with the slide retracted.