I don't see how any statistics about this could even be reliable... how do they know the children wouldn't have ended up being bright anyway? I don't think breast is best even if it does rhyme
I think bottle is best because it's generally easier to adapt to for most women and avoids as much stress. Lots of mothers get really worked up about breast feeding and it's just not necessary.
Milk formula isn't going to make your baby lack intelligence, so unless there are medical reasons for not using it like allergies then I think every mum should feel ok about using it.