Opinions on best formula for spit-up issues?

help! my 3 1/2 month old is severly constipated on soy formula and we need to switch her back to milk-based. the reason for the soy was that she spit-up the milk-based...it just didn't seem to agree with her tummy i guess. but, after a very scary constipation experience, we need to switch asap. anyone have any experience with a formula that didn't cause a lot of spit-up or constipation? we've tried gentlease a few times and good start once.