Which formula is best for newborn ? why are so many products out there?

Please ask you doc: Your newborn's doctor should be able to fully discuss that with you and if the doctor won't , you need to find a new one, that is their responsibilty to discuss which one is best for your child. Just like any other business there are many companies that make formula since it is a big industry.

There is no best: Breast milk is the best but if you are going the formula route then it depends on the size and gestational age of your baby as preterms and late preterms need transitional formula rather than term formula. Also, it is important for the formula to be iron fortified.