The main difference between Enfamil Enspire and Similac Pro Advance is inclusion of lactoferrin and MFGM.  Similac Pro Advance instead has is a probiotic called 2'-FL HMO, also found in abundance in breastmilk.  Similac Pro Advance also has a few other ingredients not found in Enspire such as the antioxidant lutein which helps with brain and eye development. It contains high oleic safflower oil instead of  palm olein oil which is a huge benefit.  This is a better fat option as it doesn't inhibit calcium absorption.  While this a safe source of fats, there may be some longterm heart disease risk.  As for similarities, both formulas offer DHA, prebiotics, and very similar amounts of vitamins.  Also, both include lactose and whey protein concentrate.  Similac Pro Advance lacks a source of ARA.  However, it does offer a significantly higher amount of inositol for brain health. It is also higher in sodium.  The FDA has recently proposed lower sodium intake to promote better renal and cardiovascular health. Essentially, both infant formulas are are wonderful options with different pros and cons.  We prefer Enfamil Enspire because of its unique ingredients, but Similac Pro Advance is significantly more affordable.  See more formula comparisons in our Similac vs Enfamil article.