The easiets factions are Date, Shimazu and perhapd the Mori. I think we can all agree on that perhaps?

The hardest factions are The Hattori (they reach realm divide in like no turns), the Tokugawa (being a vassal sucks, aswell as having other powerfull clans 1 turn away), and the Uesugi (starting location, crap diplomacy becomes your doom)