I was sitting at my desk at work today trying very hard not to listen to the conversation happening behind me. Two of my coworkers were debating whether frozen fruits and vegetables are as good for you as fresh ones. I only lasted a few seconds and then I spun around in my chair and jumped into the fray.
It seems like a reasonable assumption that frozen vegetables wouldn't be as good for you as fresh ones, because who knows how long they've been in the freezer? There are two problems with that logic: 1) freezing food tends to arrest the rate of decay, locking in whatever vitamins and minerals are in there, and 2) frozen foods are usually closer to being fully ripe when they are picked.
Large growers often have clients that are hundreds or thousands of miles distant from their farms. If they want their fruits and vegetables to look good on the grocery store shelves, they have to be picked green and shipped. They ripen on the way and they look good for a few days in the store. Growers that are freezing their produce can let it ripen on the plant, pick it, pack it, and ship it frozen.
If you have a farmer's market handy, picked ripe and still fresh is the best choice. If you can only get to the grocery store, frozen often beats fresh for ripeness and nutrients. Who would have guessed?