for the first 6 months or so my twins (who were 2 months preemie) could only stomach Enfamil Gentlease. it was so expensive! around month 7 they were finally able to tolerate 'normal' formula, and once that happened, we immediately switched over to store brand and saved HUNDREDS of dollars a month. the best deal was to go to the price club (like a Sam's or Costco) and get the giant cans of formula. and FYI for anyone whose babies do well on Gentlease, they now offer a comparable product at Sam's (look for the purple colored can). they just started selling it a few months ago as far as i know, and boy do i wish they had had it when my twins were newborns.
I did buy the parent's choice brand yesterday but I feel kinda bad. I figured it was fine...he is 11 months this wednesday so we have a month left and are kinda low on money so I did it! I did compare the ingredients though w/the Enfamil I usually buy! LOL. Like someone said you just can't help it!
I say if the ingrediants and the nutritional value are the same, go for it. You will know soon enough whether or not the baby will tolerate it. Im sure that in your own diet, you have selected store brands vs national brands. The store brands are usually very similar in taste to the nationals. Do for your baby, as you would do for yourself.
When in doubt, as the pediatrician.