find out in advance which professors or sections use Open Educational Resources. Any time you have the option of picking the OER section, take it. Not only will you save money, but you’re more likely to get the benefit of a professor who went the extra mile to help students. It’s not a perfect barometer, but it’s a better-than-random indicator that this professor is particularly engaged in the course. When professors have helped curate, assemble, or even create the material themselves, they’re invested in it.  In my observation, faculty passion for a subject is contagious. Give me a passionate professor with pretty-good OER over a dutiful one with a solid commercial book any day of the week