Here are some brands of supplements that I think are high quality:

AOR http://www.aor.ca

HepaPro http://www.hepahealth.com/hepapro_product.htm

Now Foods http://www.nowfoods.com

LivOn Labs http://www.livonlabs.com

BodyBio http://www.bodybio.com

Nutricology http://www.nutricology.com

Jarrow http://www.jarrow.com

VSL3 http://www.vsl3.com

Proferrin http://www.proferrin.ca

These are based in North America. I'm not sure what the situation is like in other parts of the world. This is not a complete list by any means, just an example of some companies that I think produce at least one high-quality product.

Even though I listed some brands above, different brands optimize for different things, and people can react differently to the same supplements, so most of the time, trial and error is needed to figure out which supplements work for a particular individual.

Here are some things I take into consideration when choosing supplements.

1) There are two mutually exclusive approaches to creating a herbal supplement (more than two actually, but I'm simplifying to make a point.) One approach is to focus on getting as pure and measureable an active ingredient as possible. This is similar to how one would approach making a prescription drug. The other approach takes the view that we as a society do not yet understand all the nuances of what makes a herb work, and that isolating an active ingredient, or optimizing for it, may reduce the effectiveness that the combinations of substances in the herb have in its unaltered proportions. So the aim of this approach is to present the herb in its most unaltered form, which means that there can be more variations between batches.

So, from my list above, AOR takes basically the first approach, and HepaPro takes the second approach. I think that both approaches can be useful.

There are also a whole bunch of companies whose approach seems to be based on marketing, cost-cutting, and mediocrity, but I don't think any of the companies I mentioned above fit in that category.

2) Some products have been studied by scientists. For example, some specific strains of probiotics sold by Jarrow have papers published about them.

3) Reading the ingredients is really important. It helps to know:

a) the form of the substance b) the amount of the substance c) the type of fillers and additives used, if any.

There can be a lot of variation in those three things. For example, Vitamin B5 could mean pantothenic acid or pantethine. A probiotic supplement could have 5 million organisms or 5 billion organisms, a difference in amount of a thousandfold. A herbal supplement could have methylcellulose filler, or natural flavoring added, or no additives or fillers at all. These things can make a difference.

4) When choosing which form of a substance to take, and if going with the approach of seeking a reliable amount of an active ingredient rather than the whole herb, then it usually makes sense to choose something that is closer to what the body would actually use than something that is a precursor to what it has to produce eg. pantethine instead of pantothenic acid. This is not always a useful rule of thumb, and sometimes there are substances that cannot be absorbed by the body through the digestive system if too close to the final substance. However, the reason it can be a good idea is that sometimes the reason a person is deficient in a substance is that something has gone wrong with the body's ability to make the final substance from a dietary intake of the precursors. So adding more of the precursor would not fix the problem. And even if that process works, it might take more energy for the body make the final substance, which could tire the person out, or the precursor may not be absorbed as well.

There are other considerations to take into account when choosing which form of substance to take. For example, BodyBio makes different forms of Butyric acid. Some with just sodium, some with just potassium, and some with a balanced amount of sodium and potassium. Depending on what the balance of electrolytes in your body tends to be, you can choose which one suits you best. For most people, I would guess that the balanced amount of sodium and potassium would be the best option, but there are circumstances that would make a different choice better.

5) Personal experience usually trumps how good things look on paper.

I have noticed differences in how I feel, taking different brands and formulations of supplements. For example, I feel a noticeable difference from taking the LivOn Labs lypospheric vitamin C than I do from straight up ascorbic acid from AOR. It seems to have a better effect and to act more quickly. I'm not totally happy with LivOn Labs as a company, since they add extraneous additives and flavourings, especially to their other products. They don't add as many to the vitamin C. I'm not entirely sure whether the effect I feel is from the vitamin C itself getting to the site better because of the lipids surrounding it, or if what my body actually needs more of are the lipids themselves.

VSL3 stopped persistent diarrhea while I was on antibiotics when no other probiotic did. I think this may be because each packet has about 450 billion organisms, which is much higher than any other product on the market.

Those are experiences where I can point to a difference between brands and formulations. But sometimes, there isn't as easy a difference to point to. I just can tell that it feels different to take one brand than another, and I don't know why, or which of the differences in the ingredients listed on the package, or differences in the manufacturing process, might be involved. It helps to pay attention.

My preference is for Life Extension Foundation. Large org with a mission beyond money.

For general manufacturers, I go with Now Foods, a large and US based company. LEF carries some of their stuff.