I'm torn between the Ronin and the Speaker. On the one hand, the Kurosawa-esque feel of L5R is one of the things I love about it and while ronin have never been mechanically represented well until 5th edition, the story of the wandering ronin who walks into town and upends the established order by helping knock down a corrupt official fits this feeling completely.
On the other hand, the Speaker gives all sorts of possibilities to deal with ancestors upset at their descendants, hungry ghosts warped by their own actions in life, animals spirits enraged at humans showing disrespect to their lands, and even the demons of Jigoku. In many ways the Speaker is in just as good a position to upend Rokugani society in such a way as to protect those within it who are decent to other people and punish those who are not.
So, with that in mind, I think I'm going to go with...
[X] The Speaker
Because I think it opens up a lot of fun ghost stories, though it was a hard choice for me because I love Ronin. EarthScorpion's reasoning has convinced me, however, and I think it would be neat to explore a Shugenja who has avoided being snatched up by one of the Clans. Much like with Ronin it makes people suspicious, and also like Ronin I think there's enough connection to Rokugani society with the Speaker that the character will become an agent of change wherever they go.
Which is, ultimately, what I'm looking for.