CNN has a co-article with Real Simple magazine which breaks down the different kinds of vitamins.  Each kind of vitamin gets three bullet points: "What they are," "Benefits," and "Keep in mind."  This is puff piece reporting at its finest, since nowhere in the article does it question the wisdom of taking a vitamin at all, much less pit different kinds of vitamins against each other in a meaningful way.

A disinterested reader might come away from the article with an impression that all vitamins are pretty much the same.  Some contain a little bit more of one vitamin than another, or come in an easier delivery system.  (For example, I know a lot of people who don't like to swallow pills, and prefer chewable adult multivitamins.)

The biggest issue with vitamins is whether or not ingesting vitamins in pill (or powder, or packet of gel caps) form even does any good.  I was shocked to discover how little data there is to back up the assumption that you should be taking a vitamin supplement.  

We don't have a lot of science to back up the very idea that you can separate the vitamin (e.g. lycopene) from its source (tomatoes) and have it be absorbed by your body in any meaningful way.  We know that when you eat a tomato, you get lycopene, and that lycopene is good for you.  But that doesn't mean that you can take the lycopene out of the tomato, manufacture it in a chemical plant, deliver it by a pill, and expect the same effects.  Nutrition is not a matter of algebraic equations.  

In fact, specifically in the case of lycopene, it turns out that lycopene levels in the bloodstream do not get elevated by taking a lycopene supplement.  Not to nearly the extent they do when you eat a tomato.  Something about the process of eating that tomato puts the lycopene into your bloodstream, and it doesn't really work if you distill it down to pill form.

For how many other nutrients is this true?  Frankly, we don't know.  And there isn't a lot of research money pushing to find out.  Vitamin supplements are big business, whereas the opposite (taking down the vitamin supplement industry) is not true.  Who would gain from a study showing that vitamin supplements are useless?  

This is aside from the issue that we don't know how much of a vitamin you ought to be taking in the first place.  Most of the RDA numbers are from a bare survival perspective, and date from the 1940s.  Government scientists found that if you get less than X% of nutrient Z every day, you get sick.  Therefore, they set X% as the minimum daily requirement.  Somewhere along the line this became the Recommended Daily Allowance, for no particular reason except that it's the data that we had.  

It turns out that the best way to get your nutritional requirements met is to eat a boring old diet, like your grandmother would have recommended.  Whole grains, fruits, vegetables, complex proteins (either from vegetarian or animal sources), and a variety of all of the above.