None. No research data has shown that a daily multivitamin in an otherwise healthy individual will reduce disease burden or prolong life. It is by far best to get your nutrients by eating a healthy diet full of fruits/veggies, lean protein, and dairy. Also, nutrients obtained through food instead of a vitamin are better absorbed.
You may not need it. Every other day is very safe. With a mixed healthy diet probably not helpful.
Any. Guidelines indicate that most adults should take a multivitamin, but there is no evidence that any specific brand is superior. I usually advise patients to shop by price for an adult vitamin, and compare labels with brand names- the nutrients are usually listed in a way that you can easily compare to be sure they're the same.
Vitamins. Most people falsely overvalue vitamins you don't need any supplements if you eat a balanced diet broccoli/spinach for vit b, carrots/corn for a, and citrus for c works pretty good. Vit d is tricky because most people don't drink enough milk; alternates include some yogurts, mushrooms, etc. One multivitamin is sufficient to take.
Real Food. Americans have world's most expensive urine because we believe that there is something easier than a good diet to keep us healthy. If you eat a diet rich in a variety of fruits and vegetables, adequate calcium, lean protein and fats like olive oil, you will get your vitamins. If you are eating an unbalanced diet, no vitamin will make up for that. Write down all you eat for 1 wk & talk to your md.
A good quality MVI (multivitamin) Some multivitamins are of poor quality and are not absorbed, so I do not recommend shopping by price. Try to look for standardized on the label to show some quality control. Otherwise I have recommended several brand names. I do not like a multivitamin with iron because iron can inhibit absorption of some other vitamins. Take iron separately if needed.