I have tried GNC 100% whey, EAS Simply whey, and Optimum Nutrition's 100% whey. I like the taste of EAS best so far. I only bought it because I got it cheap from a link here at some point. I bought the vanilla. Optimum Nutrition came in a close second, but GNC brand wasn't that bad either. GNC is the most expensive of the three, but I got a good deal on it when I bought it. (Are you seeing a pattern here? lol. Whatever's cheapest works for me.)
Oh yea, I've also tried ProMax Banana and BLECH....GROSS....EWWW...YUCK.
I have 5lb tubs of Optimum Nutrition Vanilla and EAS Simply Whey in Chocolate on my fridge right now. I hate the taste of the O.N. vanilla. I like the choc EAS protein. The O.N. tastes VERY chemical.
I have found that 3 scoops of Simply Whey with a glass of choc milk and about 5 big ice cubes tastes pretty dang good. Both brands are about the same in cost and value, so taste matters.