Google Maps has better satellite and air photos that show more places.
Bing Maps has maps that are more detailed, have more layers, and are easier to use.
Google Maps has more features, like information about traffic, details about where you are, street view, and directions for public transportation.
Bing Maps has a view from above that lets you see buildings and other landmarks in 3D.
Google Maps estimated how long a trip would take based on how busy the roads were, but Bing Maps does not.