If we consider that in principle:
a) Dominant thinkers repress their feeling function stronger than dominant intuitives.
b) Extraverts are concerned with the outer (objective) world and introverts are concerned with the inner (subjective) world.
Theoretically, it would be the ENTJ that is the most objective, having as dominant function Extraverted Thinking.
However, in order to properly answer this question we should measure people's personality type along with their objectivity and determine if there is a relationship between the two.