Which is better frozen foods or fresh food that has travelled?

A while ago, an ad campaign ran in the uk for either birds eye or youngs frozen fish. It seemed to prove scientificly that frozen fish was just as nutritious (with vitamins etc) as when it was frozen. It also showed fresh food that wasn't frozen but transported fresh and arrived in a poorer state than the frozen food. I always thought that the perceived wisdom for this was that freezing distroyed the vitamins and such, but this ad changed my view.
Now there is an ad campaign for morrison's which says they would never freeze their fish.
Which is better?
By all means state an uninformed opinion or a gut feeling if you just want 2 points, but I'd prefer a scientific anwer if possible. Thank you
Sorry, I'm not at level two yet so I can't give thumbs up as yet, but both the answers so far have been excellent, exactly what I was looking for and something I can quote too as I intend to contact Morrisons with this at the end . Thank You

having worked as a dietetic technician most of my life' frozen food not only retains the vitamins and minerals in the food but it is also much safer to eat. Non frozen meats and fishes can be handled sloppily and can cause food poisoning.
all frozen foods must be examined to be sure that it has not been frozen then thawed and then refrozen for maximum safety.

I don't know if its a "scientific" reason, but Alton Brown the tv chef says that these days freezing techniques are so good that you eliminate a lot of the freezer burn and drying out that used to sap the moisture and nutrients out of frozen foods.

He also recommends that if you intend to buy meat and fish at the market, fresh or frozen, you should put a small cooler in your car to carry it home in or get one of those thermal bags to preserve the freshness of your food and prevent bacteria growth.

Sounds reasonable to me.