It depends on what you're going for. I've found that CS2 Livetrace works pretty well for hand drawn illustrations - I have a couple examples in my Portfolio:
Click on Pirate Zombie Skull and Skateboarding Bird Monster, both were hand drawn and livetraced. I thought the conversion was pretty good -
Aaron Ray | Design Illustration Motion
But if it was a cleaner image with staight lines I think the pen tool would work best.