This slogan is very popular. It is true and it will remain true until the science haven’t invented an exact replica of the milk from mother’s mammary gland:
BREASTMILK STILL BEST FOR YOUR BABY UP TO TWO YEARS OF AGE.
All the doctors and medical associations agree to this slogan. Even the commercial infant formulas have this slogan boldly imprinted on their label.
However, the said slogan is only true if the mother is healthy and producing an ample amount of milk. There are cases when milk is not suitable for baby, producing little amount or no milk at all. Then you need to search for the right commercial milk formula for your baby.
This standard by Codex Alementarius may help you decide. Reading this article might be a hard task but it will benefit you adorable baby in the end.
STANDARD FOR INFANT FORMULA AND FORMULAS FOR SPECIAL MEDICAL PURPOSES INTENDED FOR INFANTS
Full document can be read here.