From my understanding, frozen can have more vitamins than fresh, depending on where your store gets their produce from. Frozen veggies are picked, sorted, washed and frozen w/in a few hours, locking in all the vitamins. If your store gets local produced, they are picked, sorted, washed and put on the shelf w/in hours so it is about the same. If your store is shipping in produce, then they are picked, sorted, washed, sit in a warehouse, sit on a truck, and then stocked on the shelves. The sitting around causes them to lose some vitamin content.
I live in the Midwest, so fresh, local produce isn't going to happen year-round. I try to buy local in the growing season, and frozen during the off season. Fruit, I always buy fresh, even though I know its shipped in a lot of the year, but I try to buy whats in season, it tastes better. To me, fresh and frozen veggies taste fairly similar. The canned crap is well, crap. Mushy canned veggies with weird colors - yuck! No wonder I didn't like peas and asparagus growing up - it was the odd can shade of grey-green slime. ewwwww!
Nan