I dumped Yoshimo for Jan and I was glad that I did. Jan has very amusing dialog, and I got really annoyed by the "I can dance on the head of a pin" commentary. As for skills, Jan vs. Yoshimo is a matter of how you play the game. I never backstab, and thus Jan is the better thief (infinite money if you want to abuse the game a little). And, my main character was a barbarian, so I didn't need Yoshimo's fighting skills, but instead needed Jan's spell-casting ability.
"But I also made it clear to [Vladimir Putin] that it's important to think beyond the old days of when we had the concept that if we blew each other up, the world would be safe." -President George W. Bush, Washington, D.C., May 1, 2001