Wow, good question! My daughter is allergic to milk, so we didn't even have the option of giving her milk after one year. What does your doctor recommend? After a year old, I know many babies go on to whole or 2% milk. Mainly for the fat content. Since our daughter can't have milk, we increase her healthy fats with avocado. Organic milk would be a good option if you are concerned about hormones....studies have shown that the hormone levels in milk are causing young girls to hit puberty earlier.
If your son is on milk based formula, than go to milk, unless your child's doctor recommends something else. Our 16 month old is on the Similac Soy Based Go and Grow which is less expensive than regular formula. Actually, since the formula makes so many bottles, it may be about the same price as milk with the way the economy is going! Lastly, since your son is a year old, you can switch out many of those "milk" feedings with water. He won't need as much milk as he gets older. I hope this was helpful!