Per several on here, different brands have different recommendations. My last batch, I used Dumor brand. They have a starter and a grower, different blends. I have to say I'm not happy with the brand; I've had two cockerels that had feather issues with it, so I switched to Kent; I'm happier with Kent, but it has only one formula.
Oh, and I've also fed Purina - seems like most of them recommend feeding starter OR grower until 18 weeks, then switching to layer formula.
Oh, and I've also fed Purina - seems like most of them recommend feeding starter OR grower until 18 weeks, then switching to layer formula.