I was gonna say the same thing, you beat me to it.
I'd put my money on sand though. The Milky Way has 200-400 billion stars... I saw an interesting graphic about money (found it: [link]) and since 100 grains of sand are smaller than a 100$ bill, and the fact that deserts are huge, sand grains are definitely in the trillions and possibly quantillions. So sand wins.
Oh wait, I just reread your question, I was thinking about the number of sand grains vs stars in the Milky Way, not the universe. Yeah wikipedia says there's probably over 170 billion galaxies. So stars win.