A lot of you seem to be under the assumption that psych is "more" feeling oriented, more about "loving others" plus Freud stuff or something, and that hard-nosed empirical minds have no place in the psych field. This is not so.
Trust me, an INTP can LOVE psychology once they have thoroughly studied William James and Skinner. Even if these scholars were too reductionistic about human minds, psyches what not, behaviorists do a very keen job of cleaning up the "muddiness" spoken of in psychology, leaving a pure empircal science behind. Cognitive psych is what remains of that sterilization done by the behaviorists in psychology.
If you want to abstract more (and shoot down abstractions more) often, go psych. Bio is extremly "hard" and unmoving - the principle abstract questions surrounding biology have not changed since Aristotle.
EDIT: actually, go both and go into Neuro like I am

I am becoming.... SUPERNERD