Why Breastfeed?

KC • Proud Mama to a precious little boy & sweet baby girl, a cute fur baby & an adoring wife to an amazingly supportive husband. Psalm 20:4

My MIL has complained for the last five months about breastfeeding. She thinks it's gross and keeps trying to get me to stop. I know breast is best (if it's possible) & I do love the bonding time with my son. Just for fuel to my reasons why I prefer breastfeeding over formula would you all list some reasons why breastfeeding is the preferred way... I'd like to have a factual list to support my views when she starts in on it again.