There is a site called ConsumerLab... I used to belong. But I didn't like it that they automatically renewed me and charged my credit card without my permission.
It has also been charged that they favor "certain" manufacturers.
Some of their site is free however, so you can look there.
Some companies have GMP membership (good manufacturers policy)... and others give USP on their labels.
But over time posters here have shared experiences.
Jarrow's, was always a favorite. NOW brand, LEF, NatureMade, CountryLife, Source Naturals, Doctor's Best. But not every one is best on every thing, I've found. For example I started with Doctor's Best Theanine, then tried Swanson's Ultra, and was very disappointed, and went back to Doctor's Best.
I use Doctor's Best for all my specific nutrients now because I think they are labeling nicely, affordable etc. (theanine, R-lipoic stablized, and Benfotiamine).
I use Puritan's for my methyl B12 now, since I tested it out and it worked so well. It is really inexpensive there, esp when the buy 1 get 2 free sale is on.
I use NatureMade for my SAMe, and Flaxseed oil.
I use some brand names, like EsterC with bioflavinoids, and Mega Red Krill oil.
I don't think there is any one company that can provide everything I need. So I shop around for quality and price.