If you like the feel of a normal seat, get the Capital. If you want to copy everything that Garret Byrnes/Ruben Alcantara/Kevin Porter/Sergio Layos does and get a GT Dropnose/Shadow Slim/racing-type seat, get the SL.
i was thinking about getting the sl for my race bike, but then i realized that i can go lighter w/ an odyssey jr. and this alluminum mt. bike seat post that i had lying around. so now that stuff weighs like 10.6oz.