Which direction is "correct" for a single-throw switch?

[Uncwilly]

Originally Posted by Mark Rose

Though North American three prong plugs are often mounted with the round ground pin down, it's actually safer to have it at the top: if the plug becomes loose, it's better to have something fall on the ground pin that hot or neutral.

The mass of the plug and the fact that the ground pin is the longest would dictate that having it bottom would create a more stable connection.