I have almost all of my demo builds from gsf paradise, It's just that I combined them Into one when I got the full version. And I don't remember my first build, considering I had the demo for at least 10 times as long as I've had the full version at this point. But my favorite demo build was one with tier tactical guns and a bunch of ai's that wander and shoot you. One of my last demo builds, but MAN it was fun to just pass the time in.
SUPEREDIT: And the only server I remember out of my first few was Muffin's freebuild. We're good friends now. :D