Whats better three whites or three blacks???
Not even going to go there.
Hah! But seriously, it depends on what you are trying to do and the combination ratios. Either could work. I blended 3 blacks in my Darkest Night
blend, and it turned out great. It also would make a difference if you are including any flavored teas. Fruity light flavors work best with whites and spicy, rich ones work best with blacks -- IMHO.