I don't spend much time picking the next faction leader -- I generally just let the game stipulate who that will be.

Rather, I spend a lot of time "role-playing" a faction strategy based on the current leader's traits and retinue. For example, if a new faction leader has had high influence and a couple of "Foreign Tastes" sorts of vices, I roleplay the entire faction as diplomacy-only marshmallow who try to expand via negotiation against rebels and factions every other faction hates, and who will sell a city rather than defend it. etc etc. With maybe a rebel family member who's got high command and just wants to smash the other faction.

Makes for some amusing moments!