Breast-feeding's best for baby, the American Academy of Pediatrics (AAP) says. "But when breast-feeding isn't an option, choose a formula that most closely mimics breast milk," says Sharon Collier, R. D., pediatric nutritionist and clinical nutrition director at Children's Hospital Boston. Look for the following must-have features:

Cow's milk base
About 35 percent of bottle-fed babies consume at least some of their protein from soy. The AAP recommends that all infants who can't be breast-fed drink cow's milk formulas unless it's medically necessary to make the switch. "Soy-based formulas don't have lactose, which is known to help improve calcium absorption and is present in breast milk," Collier says. Plus, soy-based formulas exacerbate osteopenia, a poor bone density condition in premature infants, unlike cow's-milk-based formulas, according to a 2008 AAP review published in Pediatrics.

Iron
Babies need iron to help their brains and bodies grow, as well as boost their oxygen-supplying red blood cells. Any standard cow's milk formula will contain enough iron, Collier says. "The total amount is much higher than what is found in breast milk because the iron in breast milk is very efficiently absorbed," she says.

DHA/ARA
These omega-3's (DHA) and omega-6's (ARA) exist naturally in breast milk and may aid in brain and eye development. A 2009 study review found that infants should receive feedings with at least 0.3 percent DHA and a level of ARA equal or greater than the DHA level.

Choline
This nutrient helps strengthen your child's cells and jumpstart the central nervous system. "Infants have a greater need for choline because of rapid brain growth," Collier says. Standard formulas contain 81 milligrams of the nutrient per liter. And specialty formulas, like those for premature babies, contain even more.

Bottled bull?
If a company sells baby formula in the U.S., the stuff must meet basic nutritional standards. "Words like 'premium' or 'comfort'—much of this is marketing," says Sharon Collier, R.D., clinical nutrition director at Children's Hospital Boston. "Your basic baby formulas are all about the same." Lower your costs by purchasing cans of powder, which are less expensive than the single-serving packets, and easier to pack than ready-to-feed or liquid-concentrate varieties, Collier says. Also, be cautious of formulas specially designed for children 6 months and older. "They're marketed as a way to get around picky eating," Collier says. "From a clinical and expense point of view, they aren't necessary."