When taking vitamin which one is best to take A B C D or just multivitamins?

All are needed so... By definition all vitamins are essential for health so they are all important. Deficiencies of each are common, so I advise a good quality multivitamin. See http://drrandybaker.com/2014/01/ for details. While it is possible to get most vitamins with an exceptional diet, in fall and winter most Americans need D as we can't get enough from the sun. I advise extra D3- 5000 iu/day in fall & winter.