This is a very interesting thread, especially since I have observed that most discussions (scientific and non-scientific) wind up at defining terms, if allowed to run its course.
My opinion is that we need three words to adequately describe judgments or comparisons commonly made in the audio world when evaluating equipment. Let me qualify that these definitions assume that the person(s) making the observations are acting in good faith and are not trying to deceive for personal reasons (such as advertising, sales, ego, etc.) The problem is that no definitions are perfect and it is hard to get a consensus.
Objective – judgment or results not influenced by individual biases, personal feelings or opinions in considering and representing reported “facts” or parameters. These usually involve scientific instruments.
See also:
https://en.wikipedia.org/wiki/Objectivity_(science)
Subjective -- judgment or results that may be influenced by individual biases, personal feelings or opinions (when attempting to be objective) in representing “facts” or parameters. (Bias as used here is not a negative term, as all humans have subconscious biases and are very difficult to exclude when trying to perform objective testing or evaluations). An "objective" result may later be found to be influenced by bias and be subjective.
Opinion -- a judgment formed about something, not necessarily based on fact or knowledge and can be (legitimately) based on personal preference
Generally, in science, opinion plays a very limited role in reported results. It is limited to such things as the potential or value of the results of an experiment. In the audio world, opinion plays a big role. For example in this blog, individuals give their opinion as to what songs, works, equipment they personally prefer.
See also:
https://en.wikipedia.org/wiki/Opinion