About Total War ii campains

I'm new to the total war series and when I open the game i'm a bit overwhelmed by the number of selectable campains. I can select original, emperor, sparta, hannibal, gaul. My biggest doubt is the difference between original and emperor. I heard that time ago the game wasn't really good until they updated to the emperor edition, my question is: selecting original let me play the old game and emperor the game with the emperor update or has nothing to do with the updates?

Also what are the best campains or a good order to play them?