Should I choose an tenured advisor good at research but bad at teaching or an untenured professor good at teaching?
I'm not sure why a professor's capabilities as a lecturer should have anything to do when considering her competencies as a mentor and research advisor. The two skill sets are almost completely separate from one another. Moreover, if part of your concern is that you want to become a teaching faculty member some day, then there's probably a chance to be a teaching assistant for another faculty member who is more qualified as a teacher (such as your Professor B).