This is the way I look at it. As long as the processing hasn't removed or added anything, then I would consider it to be whole. For example, if I took whole unprocessed oat groats and put them in my vitamix and blended them into flour, I would still consider them to be a whole grain, as nothing was added or removed. So, for me, steel cut oats, rolled oats, thick rolled oats, quick rolled oats would all be considered whole grains. Since rolled oats and quick oats are steamed during processing, they probably lose a small amount of their nutrients. It would rate oat groats and steel cut oats at about the same level of nutrition, as the steel cut oats are very minimally processed so have lost little, if any nutrition. However, pick the form that you are likely to eat the most of, as that will probably result in you getting the most nutrition.