Fresh Grown or Powdered: Which is best?

I want to write a bit about about whether it is better to grow, juice and drink your own wheatgrass or buy Wheatgrass Juice Powder. Many people say that you need to drink it fresh within minutes of cutting and juicing it to retain the vitamins. I grow my own wheatgrass and drink it fresh every day, but I am not a chemist, and don't analyze the nutrients of my own wheatgrass. All I know is that it tastes pretty good and I feel fine drinking it.
That said, I have come across a few websites that say that growing wheatgrass in trays gives you far less vitamins and nutrients than wheatgrass grown in the ground. This website claims that wheatgrass should be grown for 200 days in a cold climate, planted in the fall and harvested in the spring when it is 7 inches tall or so. They say this way provides the ultimate in nutrients and is far superior to wheatgrass grown quickly in trays. The website also claims that the grass has been exposed to the sunlight for 200 days so it has a lot more chlorophyl. My logic tells me however that it is only exposed to sunlight once the snow on top of it melts, the seeds sprout, and the grass grows. This period of time probably isn't very long, although it is most definately longer than the grow-in-a-tray method. Another inherent problem with this method is that the wheatgrass can only be harvested for a few days each year, so it is impossible to get it fresh for about 362 days of the year!!! They cut it, juice it, make it into powder, or bottle the juice.
The big question to answer is this: Is it better to grow, juice, and drink fresh wheatgrass that just grew, but has fewer nutrients, or is it better to drink wheatgrass powder that was cut nearly a year ago? I guess I would like to see someone who know what they are doing do a comparison study of these two. For now though, I will keep on growing and drinking my own stuff, mostly because it is more fun and meaningful to me. I figure I can easily drink twice as much if I have to, thus doubling the nutrients I receive, and probably narrowing the gap between my home grown grass and the powdered stuff. Like always, feel free to comment if you have any input on this subject.