Certainly there must be courses that you >need< to be taking in order to be on track with a science series ; if you're in your first two years then you'll most likely just be filling your schedule with pre-reqs. If you can afford putting off a class for a better professor, then I think that would be wise. If you would be a little bit behind by delaying a class in order to take the better professor, I think I would still do it. This past quarter, I thought I would be able to handle a certain math prof despite his terrible reviews, and I had to pay the price. Take your peers' advice.. if there's a terrible prof out there, don't try to be the one to beat the odds against them.