Depends on what you need them to do. Play an instrument? Gilmour. Write lyrics? Waters.
I'll go with sell overall. For better *and* worse, Waters was more of the architect of the band's style in the post-Barrett years. Gilmour was more of an architect than Waters will ever admit, but Waters probably did more.
Favorite Waters song? "Set Controls for the Heart of the Sun", "Careful With That Axe, Eugene", "Dogs", one of those probably.