According to Kaplan MTB 2CK, they'll generally test guidelines from USPSTF because it's a non-biased source. Specialty colleges tend to make more aggressive screening recommendations because they are specifically interested in one particular disease, even when there isn't evidence to support their recommendation (i.e. PSA, mammogram before 50, etc.).
In general, I'd go with UW over a textbook. Your textbook is there to help you become a better doctor, but it might have several layers of information that will only complicate what you need to know for the USMLE.