For vitamin B3 supplementation, both niacinamide (nicotinamide) and niacin (nicotinic acid) are equally good, it is only inositol hexanicotinate that may not be suitable. The biological activity of the latter is so low that it is questionable whether it can be considered a source of vitamin B3 at all. In addition, inositol hexanicotinate is the only form in supplements that is foreign to the human body and is metabolized in an unnatural way (an exogenous substance circulates in our bloodstream for more than two days and it is questionable what percentage of it is broken down into niacin and inositol, and what percentage remains in the form of inositol hexanicotinate ester).  

Types of vitamin B3 

Vitamin B3 can be obtained naturally through diet in 5 different forms: 

1.) From niacinamide: 

Animal source foods contain almost only this form, and a lot of it. (By the way, plant source foods also contain this form, and certain plant source foods contain a lot of it.) 

Specifically, B3 is already present in "active" forms, i.e. coenzyme forms, the so-called pyridine nucleotides (NAD+/NADH and NADP+/NADPH) in animal source foods (and to a large extent in the plant source foods mentioned above), but these "active" coenzyme forms must first be degraded to niacinamide before they can be absorbed. They are then degraded to niacinamide and then converted back to their active forms (NAD/stb) after absorption. [1,2,3]   

2.) From niacin (also known as nicotinic acid): 

It is present in plant source foods, but in many cases it is not, or only slightly absorbed. [2,3] 

3.) From niacinamide riboside and other B3 derivatives: 

It is mainly found in milk, but is also present in other animal source foods. Unfortunately, there is only a very small amount in any food source. [1,3,4,5] 

4.) Converted from amino acid tryptophan [1,3,5] 

5.) Converted into short-chain fatty acids from fermented fibres by bacteria. 

(Moreover, some short-chain fatty acids, such as butyrate, can themselves induce B3 activity, although in a slightly different way...) [5] 

In practice this means that if you follow a natural diet, if you eat meat/fish/eggs or anything of animal origin on a daily basis, almost all of your B3 source comes from niacinamide. That is, of course, if you are not vegan. So, by default, our meat-rich diet will result in 90% niacinamide + 9% niacin + 1% other vitamin B3 intake. For vegans, only about 50% of B3 may come from niacinamide, but it can be more or less. 

If someone's diet is deficient in vitamin B3 (which is practically only the case among the poor in the third world), then B3 production from tryptophan and with the help of bacteria, from fibre, is increased, so in such cases a small amount of vitamin B3 is all they get, the sources of which are tryptophan and fibre. Overall, niacin from food, and niacinamide account for about 99% of our B3 intake, of which niacinamide accounts for 90-99% if we eat animal source foods regularly. And the same is true to natural peoples, and our ancestors also has a similar diet. 

Forms of vitamin B3 available in food supplements and their metabolism 

In dietary supplements, theoretically, niacin (nicotinic acid), niacinamide (nicotinamide), inositol hexanicotinate and niacinamide riboside are used (the latter is not practically used, but I will not go into that now). Of these, only inositol hexanicotinate is foreign to the body as a molecule.  

Since in a natural diet only niacinamide is present or only in minimum dominance, this or a mixture of it with niacin is the most natural supplementation solution if you are trying to imitate natural balance, which I think is always the right direction. 

I won't go into details in terms of their metabolism, it's quite complicated, but briefly: 

After absorption of ingested niacin (nicotinic acid), a significant part of it is converted to niacinamide and finally to active coenzymes. (They can also be converted to active coenzymes without being converted to niacinamide via another pathway.) [1,3,5] 

The ingested niacinamide is partially broken down in the digestive tract into niacin (nicotinic acid) before it is absorbed, so even though we have ingested niacinamide, some of it is absorbed as nicotinic acid. [3] I know of no evidence that niacinamide cannot be converted to niacin in humans. Even if there were, it wouldn't change anything, because we don't need nicotinic acid separately, just to make niacinamide and NAD, which are also made from niacinamide.   

Both niacin and niacinamide have a fast half-life and are perfectly absorbed up to 4000mg. [1,3] This means that after a B3-rich meal, blood levels of niacin/niacinamide spike and then plummet within a few hours. [1,3] There is no source of B3 in nature that would provide a constant, consistent level of B3, it would not be natural and would raise the problem that Paul Jaminet presented in his book, The Perfect Health Diet, in chapter 'Chronic Origins of Disease': Vitamin B3 also supports the pathogens that cause chronic infections, so it is worth providing it for as short a time as possible. A long-acting B3 formulation can be particularly problematic, since in case its level rises and falls suddenly then it is available to parasites/bacteria for a short period of time, whereas if it is continuously at a constant level then it provides constant supply, while our own cells are obviously adapted to only having B3 for a short period of time, as there was no way to achieve a constant B3 level until a few decades ago. The goal is to have a good supply of B3 for our own cells and not for our pathogens... And this is where we come to inositol hexanicotinate. 

Problems with the inositol hexanicotinate form 

Inositol hexanicotinate is a compound that does not exist in nature, and was invented by pharmaceutical chemists with the aim of achieving a different effect on cholesterol and blood lipids from the vitamin effect of niacin in pharmacological doses, without its side effect (niacin flush). As it turns out, it has no side effects, but it has no effect either, so it's basically a dead-end experiment.[1] So they lobbied the EFSA to allow it to be used as a source of vitamin B3,[3] at least I think there's lobbying going on, because unlike the much studied and discovered metabolic niacin and niacinamide, not only there is little known about inositol hexanicotinate, but the effect/equivalence of the vitamin itself is not clear.[1,3] All that is known is that about 70% of the oral dose is absorbed, partly or wholly unchanged, as inositol hexanicotinate, which consists of 6 niacins linked to 1 inositol by 6 ester linkages. This foreign molecule thus passes, partially or completely into the bloodstream, where the 1 niacin resulting from the first ester linkage dissolution is released within half a day, the remainder circulating in the blood (now probably as inositol pentanicotinate) for at least 2 days, and it is questionable whether it will be completely broken down into niacin and inositol, or what effects its metabolites have..[1,3] From these studies, it is concluded that the release of niacin from it is only partial and/or very slow, that it appears to function as a source of vitamin B3, but that it is not known how much of it is equivalent to niacin, how much can be released and what effects it may have.[1] The only proven effect is to alleviate Raynaud's syndrome, but only at a dose of 3000-4000mg per day (as a drug called Hexopal), the mechanism behind which is unknown, whether due to its breakdown into niacin or its own unique structure.  

Inositol hexanicotinate does not have the positive effect of niacin and prolonged absorption niacin on blood lipids, although it should if it is converted to niacin in the bloodstream, so either the rate of conversion is too slow or it does not break down to niacin with the expected efficiency-> it is not a good source of B3. It is not known how much niacin can be released from inositol hexanicotinate, i.e. it is not known how much vitamin B3 it equals, so using it as a source of B3 is apriori questionable. [1] There have been virtually no new studies on it in the last 10 years and it hasn't been in the headlines, so it is unlikely that we will ever know if it is any good, or is even a source of vitamin B3. In the most recent human clinical trial, it was compared to the prolonged/slow absorption niacin, and it was found effective, while inositol hexanicotin showed no effect... [6] For my part, based on the evidence so far, I doubt that inositol hexanicotin is a source of vitamin B3 or that it has any role in maintaining health. I can only think about recommending it as a therapy, in pharmacological dosage, as a drug, for Raynaud's syndrome alone. 

Either way, I myself would be reluctant to take something on a daily basis that didn't exist a long time ago and is getting into my bloodstream in an unchanged form, circulating in it for more than 2 days, when it is not exactly known what is happening to it and what effect it is having, while there is no proven beneficial effect to make it worthwhile. So I would not recommend daily supplementation with B3 in the form of inositol hexanicotinate, although I don't think it is particularly problematic.  Basically, I think it is the high daily B3 supplementation itself that is problematic. (High daily supplementation of any vitamin B3 can increase the risk of autoimmune diseases, cancer, miscarriage, etc., as well as having a negative effect on gut flora and the immune system.[5] This includes nicotinamide riboside. I emphasize that this is only for continuous high dose (50mg+) daily use, not for intermittent use and chronic 10-20mg daily use, which I consider to have a good effect, but I will write more about this in the future...).  

Summary 

Supplementing with vitamin B3 is completely unnecessary for anyone, but if one does want to, the most natural solution is to supplement mainly with niacinamide or a mixture of niacinamide and nicotinic acid, also at a max. dose of 20mg. Inositol hexanicotinate is the least known form of B3 with the least known action and metabolism, and the only non-natural compound form of B3 that results in a steady state of foreign blood levels + also causes long-term circulation of itself as a foreign substance in our bloodstream, which may accumulate over time. Enough red signs not to choose this as the preferred form.