Supplementing with Formula

Crystal
Those of you who have to supplement with formula, what do you use?  I only use about 4-6oz a day.  I tried Similac and Enfamil regulate Newborn formula (free samples), but they tend to make her have tummy troubles!  What brand do you prefer?
Also should I do the "sensitive" version of the brand or each one has a "supplementing" version... There are just so many choices!

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