An argument based on logic and reason rather than emotion
and personal opinion is best described as objective. This type of argument
often has to do with logos, that is, reason, evidence and logic. These generally
deal with material questions or things that can be sensed or measured; things
that are associated with the real outside world, outside of oneself. The other
choices in this question: rhetoric, biased and weak do not fit with the
description that was given in the question.