Proper dose/form and method of B vits has made a huge difference in how I feel and perform in the gym. I take a multi with all the B's as well as a B complex but generally speaking those dont have the best form of B12, niacin and folate so I take them separately as well.
Plain old niacin, the kind that causes a flush, 1g 3x a day. Keep in mind not all forms of niacin are as useful as others and some even toxic at low levels.
B12 in the form of methylcobalamin AND dibencozide 12mg each sublingually. NOT all brands are created equal and just swallowing them does little good. Most multis and complexe have cyanocobalaim, junk form of B12.
Folate in the form of methylfolata, most complexes and multis use folic acid which is a poor form of folate.