FileUploader Plugin — what’s the best video format to be used for the in post media player to work?

I have been experimenting a bit, and I would like to know what is the best video format to be used for the in post media player to operate at it’s best.   I would like to work out what setting to use in a program like say WinFF http://winff.org/ to Batch convert Video media files — then to be able to use the media file with the FileUploader plugin, and to have the media play as embedded in the post.  The options are huge when converting video formats to be used on the web.  

Cheers