Least favorite faction to fight against : Egypt. They have horribly irritating archers, with heavy armors making them arrow-proof...

Least favorite faction to play : all the factions that doesn't give me the feeling of controlling a great civilization of the ancient times, either because of historical lack of relevance or culture. Or that I simply don't like.
Which includes Pontus, Britain, Armenia, Dacia, Spain and Numidia.