I would reccomend Costco #1, Walgreens #2, and then GNC #3. Costco has the best prices but very little selection. They do have MSM and I got 300 1000mg capsules there for $12 like Jerry said. Walgreens has a better selection and there is usually one brand that they have on sale. GNC has the infinite selection but you pay the price. However I do have faith that their products are top notch. I'm going to GNC to restock on some stuff tomorrow.