Do you mean for export from MixEmergency, or for playing in MixEmergency? For both of these there is no "best", and it is really up to the user to decide what they use, and what they find to be acceptable quality, and acceptable performance for their system. For example, if you have a thousands of videos, then you don't want to store them as uncompressed videos, as it would take a huge amount of spce to store them, and would case a your computer to do a lot of reading from your hard-drive.
