How do you decide whether average-risk patients should undergo annual or biennial breast cancer screening?

It's gotten really tricky in the last few years! The ACS and ACR (of course) recommend annual screening, and the USPSTF, as well as other societies, recommend biennial screening. ACS guidelines recommend annual screening from age 45-54, since it seems to make a difference in premenopausal women (both in cancer stage and mortality), and then an option to transition to biennial screening after that, when the difference appears to go away. In an average-risk patient, I usually recommend this strategy, though I am not rigid about it [i.e., if they have reasons to either avoid screening (pain, lack of money, etc.), then I am okay with biennial earlier, or if they have reasons to continue annual screening (e.g., nerves usually), then I'm also fin...