Looks are subjective, so I don’t think it’s a number 1,2, OR 3.
Some of the most UNATTRACTIVE people facially, are found to be attractive by someone else. And someone may still be attracted by someone, because of qualities other than looks.
Good character is #1. I don’t care if he’s the best learner in the world or makes the best parnassah. If he is a mean-spirited, disrespectful, inconsiderate, selfish lout, then he is worth zero as a potential shidduch. If she is totally self-centered, highly materialistic (some materialism is necessary in life, and to deny that is impractical), narcissistic, only concerned with yichus and money and how to exploit both, and not interested in lovingly raising the next generation of productive, menschlech frum Yidden, then she is worth zero as a potential shidduch.
#2 is has a good sense of humor – life throws a lot of curve balls at us, and our sense of humor enables us to get through some difficult times. Just ask Sholom Aleichem.
#3 what type of relationship does he or she have with his/her respective family? What are the parents like, and how do they treat each other? That is often indicative of how they will treat future spouses, because children grow up all too often, to be exactly like their parents, whether for good OR bad.
These three aspects are important to me. They were important when I met my future husband 38 years ago, and they are just as crucial today.