I say do not go to GNC looking for advice on what to use.It kills me how people jump on the bandwagon just to agree with others.
Yes lots of their stuff is overpriced but you can also get good deals.Go at the first of the month and see what the price is they have a set limit that they are allowed to go down on price.Even when the sell isnt on you can get the sale price most of the time.
As for their own brand not being any good check out their pro performance
100% whey.Its pretty good tasting and has less calories,carbs and sugars than most but not all.Im not saying its the best but its not bad.No I dont work for them lol.I know too much about what they sell for them to hire me haha