There is a big difference between goji berries and goji juice. The same goes for any of the new age fad products like goji, acai, et etc.... the juice is far different to the whole fruit....

It is all to do with the processing. I have a very good dvd here that explains exactly how much anti oxidant value is left in the juice after processing and for many products it is very little. There is an international standard for measuring the antioxidant value of a product and if you are really keen on the healthy stuff you should look for it on the product. It is called an ORAC score and if the product doesnt have it don't buy it is my advice.

For example, most commercial brands of goji juice when measured scientifically acutally have less antioxidant value than eating a whole apple a day.
Definitely eat the fresh berries, they are awesome.....just be aware that a lot of dodgy companies are getting on the health food bandwagon and really the juices are just overpriced crap. Not all companies are like this but a lot are.

My advice, eat the whole fruits, juicing anything loses approx 80% of its nutritional value straight up and if you do want juice, read the labels so you know exactly how it has been processed (cold pressed freeze dried stuff that has mainatined most of the fruit is what you are looking for in general).