I use S26 Gold... only as that is wot they used for her in the special care nursery inhospital and didnt see the point in changing as she seems ok on it. Haent had any problems with constipation.. but dont know if that is because she does get 1 or 2 full feeds of breastmilk a day ATM. The midwives in the nursery claim that S26 Gold is the Rolls Royce of formulas... but I guess they would say that when they r feeding it to ur child LOL