This is a question I get almost daily. The answer is not quite as simple as you may think as there are many variables to consider including price, ingredients and dietary needs.
A once daily multi-vitamin is the most important nutritional product that one can use and I can not stress that enough. Everyone, regardless of age, should be taking a vitamin supplement daily. The average person does not get the recommended daily allowance of vitamins and minerals in their diet. Most people have diets consisting of overly processed foods and / or "fast foods" that have very minimal nutritional value. The body is being robbed of essential vitamins necessary to function properly. Even if you do have a proper diet, you may still not be getting everything you need through food and a multi-vitamin is a simple way to supplement.
There are a wide variety of multi-vitamins available in the marketplace and it can be confusing. Most important is that the supplement is a "once daily" muti-vitamin. That means the product has everything necessary included in one dose. Some brand names (Centrum) will add other herbs, vitamins, etc. and market the vitamin as a "specialty 'vitamin, ex. Centrum Silver, Centrum Performance, Centrum Men, Centrum Women, etc. These additional vitamins, herbs, etc. are usually un-necessary for the average person and serve no real purpose. No need to spend the extra money. I also highly recommend vitamins for children as, again, their diets may not be sufficient for proper health. However, parents need to be aware that vitamins are not candy and that children are especially susceptible to vitamin overdose . Many children's vitamins come as gummies or chewables and kids may want more than the recommended dose. Keep them away from the kids and dose them as detailed on the label.
Another issue to consider is quality and price. Many people are not aware that there are grades of vitamins that vary in quality. The FDA does not regulate "nutritional supplements" ie, vitamins, herbs, etc. and these products can vary greatly in the amount of active ingredients and the quality of the ingredients. "Pharmaceutical grade" (A grade) vitamins will be the most expensive but the most beneficial and are usually not available in the general marketplace. They will be manufactured under strict guidelines and use higher quality ingredients. Other vitamins (B, C, D, F grade) will decrease in price and quality accordingly, however, the majority of what you will find on the shelves of your local pharmacy are safe and effective. Liquid vitamins are widely considered to be "better" because of quicker and more complete absorption but there is limited research to actually prove this to be true 100% of the time. Furthermore, adult liquid vitamins (Geritol, Centrum, etc.) can be extremely unpleasant to the taste buds. Capsules incorporate the best of both worlds as they are easy to swallow and may have better and quicker absorption than hard-pressed tablets.
Still another consideration is one's dietary and health needs. Some people may find themselves lacking in certain vitamins and / or minerals because of a poor diet or medical condition. Iron is frequently added to vitamins for those who may be lacking as well as folic acid which is important for pregnant woman. Fluoride is a common additive, along with iron, to children's vitamins to promote healthy tooth enamel. One must be aware that you can overdose on vitamins although it is extremely rare and improbable. Vitamins A, D, E, and K are fat soluble vitamins meaning that your body holds them in fat cells where they can build up to toxic levels over time, while the other common vitamins, (the multiple B vits., C, etc. ) and trace minerals are water soluble and excreted through urine, sweat, and feces. One can not overdose on water soluble vitamins. Therefor, you must be aware of any medical issues that may limit the body's need for certain vitamins as well as being aware of the amount of individual vitamins (vit. D is a good example as many people take high, once weekly doses) that you may be using.
A multi-vitamin is of the utmost importance for a healthy lifestyle. Choose a quality product at a comfortable price point while taking into account your nutritional needs.