It turns out "Breast is Best" is actually NOT the best way to talk about breast/chest feeding. It gives many parents the impression that formula is the norm and breast is just "better", and it can be demoralizing for people who cannot breastfeed.
Rather than "Best", teaching that breastfeeding is the biological norm may be a better strategy for meeting pregnant people where they are.
Talk with clients about breast/chest feeding the same way you discuss other perinatal goals and decision making- be realistic, make plans, provide resources. Start where your client is at.
Teach the risks of substitute feeding AND strategies for minimizing those risks if a parent chooses to, or must, formula feed.
Check out these videos to see a negative campaign that worked- but may not have been very ethical- and the WIC campaign "It's Only Natural".