Discussion on answer by ttw: 12 TET Interval Ranking

@Seery, but even within the standard ranking people disagree about which dissonant intervals are most or least dissonant. Also, in 12TET none of the harmonics match!!! Hence in theory none of the intervals are perfectly consonant. Folks with perfect pitch claim to be able to hear the difference and prefer to listen to Just tuned instruments. One of my physics professors in college had the problem and his wife was a professional cellist with our City's Symphony. He would "correct" her intonation by ear.