Roto-molded/plastic boards are for beginners and are inexpensive. The compression molded/fiberglass boards give the best performance all around.
Boards like the HO Joker and O'Brien Lowrider give you the biggest air. Boards like the HO Custom cut the best.
The flat nose gives you more surface area, which allows more pop off of the wake for bigger air.
Go to http://www.kneeboardplanet.com
and you can find out a bunch of stuff on kneeboards