S-26 has a bad reputation for causing constipation in babies - both MCHNs I had didn't like it at all. But having said that, most of the FF babies I know have been on that formula with no problems.

Karicare has a great reputation but smells and tastes horrible.

My MCHN liked Heinz and NAN and one of my girlfriends who is a GP is also a big fan of NAN - she prefers the HA.

Gold formulations can cause constipation in some babies.

My DD was on NAN Pro Gold with no problems, and it has a much better smell and taste than most and I understand the HA version tastes exactly the same.

I used Bellamy's Organic with my DS - it was the only one he would take - nice smell and the closest taste to breastmilk out of the various ones I tried him on. I started DD on Bellamy's too but my MCHN was wary of it just because she didn't know much about it. I eventually switched DD to NAN when we were away on holiday and the supermarket was out of stock of Bellamy's. Very similar flavour and smell and DD started sleeping through the night so I never changed her back.

Generally I seem to find that NAN HA gets the most recommendations and if I was in a position where I needed to FF again I would go for NAN.

Note that you DO NOT need to use Step 2 formula. Step 2 is casein-based rather than whey-based (Step 1 is whey-based) and harder to digest. It is good for hungry babies who are not being satisfied with Step 1 but because it is harder to digest it causes a lot of babies to suffer constipation. I would start your baby off on Step 1 of whatever brand you choose and if that is going well do not bother with Step 2. My MCHN always said that if bub is happy on Step 1 to not change...and not to try Step 2 until at least 8 months, if at all, because it is so common that it will cause constipation. The difference in nutrients between Step 1 and Step 2 is miniscule.