What's better? GNC or NOW?

I'm looking for a new whey protein and have been using GNC Pro Preformance brand for my whey, casein, creatine and mass gainer for a few years now. I got a blood test for my Vitamin D levels recently, which the mass gainer claims has 70% daily value, and the results came back very low. I know the FDA doesn't regulate supplement facts so I'm not convinced GNC is trustworthy. I started using Kre-alyne to replace GNC and it seems to be working much better, but I'm not sure what to replace the whey with. I read NOW had a good brand but I wondered if it was worth switching or if there was a better brand that still has a good price. Any thoughts?