I am 19 years old and thinking about taking a multivitamin. what is the best on the market?

No single best: This is a bit like asking what is the best cheese, wine or beer- opinions and preferences vary. But this is a good question, as some are much better than others. See http://www.Multivitaminguide.Org/ for independent ratings of 101 different brands; any in the top 30 or so are quite good; however, some of the very best, like ultranutrient by pure encapsulations, are not included on the list.