What is the best format for downloadable video?

A client of mine wants to sell video downloads. Does anybody have thoughts on the best format to use?
I’m thinking MPEG looks like it is universally supported. Are there other settings to be mindful of?

Thank you E

This might help.

Whatever suits you and the device you will be playing it in. For Notebooks and PCs its generally .AVI for Mobiles its primarily MP4