the difference is the amount of fats in the milk, there IS a slight difference in taste, whole milk will have a richer taste and have more "body" (be a bit thicker). 1% milk has only 1% of the natural fats as whole milk 2% has 2% of the fat. Vit D milk is simply whole milk with vit D added as a supplement. There is some controversy over the benefits of drinking lower fat milk over whole milk, whether it actually makes a big difference in weight or fat intake overall.
Whole milk contains 4% butterfat, 2% milk contains 2% butterfat and skim contains 0% butterfat. Contrary to popular belief, the percentage names of milk, eg 2%, 1%, are not correlated to whole milk. In other words, 2% milk does NOT contain 98% less butterfat than whole milk.
The difference is the amount of fat and vitamins that each offer. Whole/Vitamin D milk is fatty and thicker than the others. Skim is super watery and 1% & 2% are pretty much the same tasting, just different amount of fat in each!