Street only. Discounting the issue of avoiding, scaring or just being rude to the pedestrians who belong there, sidewalk riding means a curb at every corner. It also means potentially entering intersections from a place that cars don't expect me, or crossing active driveways faster and at poor angle of vision. All in all riding in the street with traffic is far and away safer, except for small children on "sidewalk" bikes.

That said, my business is on a one way street, and I'll often use the empty sidewalk for the last half block to avoiding going around the block (especially if it's raining).