A.F.
Similac caused my baby to get super constipated - and that was only on one bottle a day. She had been taking Enfamil every now and then with no problems. When I mentioned it to my best friend, she says her pedi said they're very different and not to switch between, but the generic formula from walmart is the same as enfamil so those are interchangable.
If money was no concern, I think the ready made stuff would be easier, but powder is definitely cheaper.