I like this website for vitamins / supplements - https://www.iherb.com/ they have fast shipping, and often you can find coupons. I try not to buy from Amazon because there are tons of fake, chinese counterfeit products on there (supplements included).

It's best to stay away from big-name brand vitamins like Nature Made or Nature's Bounty that are sold in grocery stores and local pharmacies. Some of those are owned by pharma companies, or similar conglomerates. If buying locally, I prefer to source my vitamins from a natural food store like MOMs Organic Market, Sprouts or something similar.

A couple brands that I've used that are good (and recommended by my holistic naturopathic doctor) are Thorne, Douglas Laboratories, Standard Process, Seeking Health, NOW Foods, and I've had good experience with California Gold (despite the name, lol).