Assuming that there are no other differences besides the salary and the advancement opportunities, I'd go with option B as well.
That being said, for someone who is nearing the end of his/her career ladder, I can see them selecting A over B.
Anyways, more relevant to the demographic of this forum, in the mix of selection criteria, I'd also consider the employer's reputation and industry recognition. I have in the past accepted positions at a lower salary because it was with a well recognized firm and could potentially lead to better opportunities after a few years.