Glass vs. build up
In my opinion, the weight savings isn't huge, but you'll definatly have a nicer surface with glass. You'll either use a little more glass to get the rigidity, or you'll use light glass, but with a handfull of formers to get the same rigidity. Either way, unless you're a pro at composites, the weight difference will be negligable.
So what are the specs on the plane? What size engine are you putting on/in it? I'd go right for the DF and forget about the prop. But that's only if you've got some experience flying. By the way, if you have a lot of things in the ducting (i.e. batteries, etc...), you could be inducing a lot of drag.
Just my $.02 worth
Russ
Oakdale Aircraft