As far as I know I think Novalac is like the best there is, though i've never used it.
S26 Gold is also supposed to be really good, but it's very rich and I've heard a number of people say their babies get constipated on it, though my sil said it was the only one that didn't constipate her kids. And i used to au-pair for 2 kids that were on it and neither of them were ever constipated by it.
We used NAN and that is also a very common one that many people use.
Two of my friends use Lactogen and are very happy with it, though i'm not a big fan of that but I don't have any specific reasons for my dislike of it.