I was reading about formula and learned that ready-to-feed is least constipating (though more expensive) while powder is most constipating regardless of brand.
I have never tried it but I know that Enfamil Reguline says it helps produce soft stools. DD has been on both Gerber Good Start Soothe and Enfamil Gentlease with no problems. She did have some constipation issues with Similac Advance.
I bf so I don't have wisdom regarding formula. My advice though would be to try other things before switching formula. I second pps who said pear or apple juice, prunes or other foods to help. Then I would talk to pedi about it.
I don't formula feed, though -- I gave it to help with spitting up, which it definitely did. I did it from six weeks through five months. It's a little pricey, but the bottle lasts about a month.
Re: What's the best formula for...