Lourdes,
I used to stick to Enfamil too (that's what the ped. recommended). Then, I did some research and found that ALL formula companies need to follow very strict guidelines. I've tried the Costco brand since they sell in bulk. I compared the ingredients, and it was identical to the name brands. We never had a problem with it. I think I first read of using generic formula in a book called Baby Bargains.
-Jen