Because I have them both in front of me:
Quaker Old Fashioned Oats (rolled)
Serving Size: 1/2 cup dry (40g)
Calories: 150
Total Fat 3g
Saturated Fat 0.5g
Polyunsaturated Fat 1g
Monounsaturated Fat 1g
Total Carbohydrate 27g
Dietary Fiber 4g
Soluble Fiber 2g
Insoluble Fiber 2g
Sugars 1g
Protein 5g
Calcium 0%
Iron 10%
Ingredients: 100% Natural Whole Grain Quaker Quality Rolled Oats
John McCann's Steel Cut Irish Oatmeal
Serving Size: 1/4 cup dry (40g)
Calories: 150
Total Fat 2.5g
Saturated Fat 0.5g
Polyunsaturated Fat 1g
Monounsaturated Fat 1g
Total Carbohydrate 27g
Dietary Fiber 3g
Soluble Fiber 2g
Insoluble Fiber 2g
Sugars <1g
Protein 4g
Calcium 2%
Iron 8%
Ingredients: 100% Whole Grain Irish Oats
They look pretty similar to me. 0.5g difference in fat, though it looks like Quaker may just have rounded up and they're actually the same. Supposedly Quaker's rolled oats have more fiber, though it looks like McCann can't add and that're actually the same too. Quaker has an extra gram of protein, and calcium and iron differ by negligible amounts. Someone messed up something because Quaker shouldn't have more fat and more protein but the same calories, but I don't think it's worth it to get upset over those tiny differences. Eat what's more convenient and/or tastes better. The stats are pretty much the same. I don't have Quick Oats/Instant Oats because I hate the texture, but the stats will be the same on them too. As a previous poster said, the only real difference is in glycemic index, which isn't nearly as important as dieters like to pretend it is. As long as you don't eat an oatmeal with a lot of added sugar, you're fine. And even then, you can do a lot worse than sugary oatmeal, and considering you post on this board, I think you can probably afford to eat 150 calories of sugary oatmeal for breakfast.