I'm going to vote "Umbrella" although it's really close between that, "Pon de Replay," "SOS," and "Shut Up and Drive." "Shut Up and Drive" is really fun and the video is damn sexy, but it feels more shoddy than "Umbrella" (plus the bridge in the latter is great). I really wish "Breakin' Dishes" was a single, though; love that damn song.