Vitamins are just supplements. You should try to get AS MUCH as you can from clean eating and use vitamins as a "touch up". Yes, if you eat 8mg of some vitamin, you probably won't absorb all 8mg, however this can also be true for food.
Eg. When you eat foods high in iron, to get as much absorption as possible, you want to eat some vitamin C (fruit) to help with absorption.
I take multivitamins, a garlic, c and horseradish, and a fish oil.
There are many arguments for and against wrt. are they useful or not, but the theory I agree with is: The more we refine natural foods, the more chance there is of removing vitamins and minerals during the refinement process.
So eat a good variety of food.
The best thing you can do for nutrition (most things actually
) is to learn about it. Learning what is in the food you eat, and what you are actually ingesting daily will help you change your eating habits for the better.