I don’t think compatibility can be reduced to the influence of one planet … but, sometimes I wonder if you should look to a particular planet over another depending on what you want from a relationship. For example, maybe emotional rapport is what you want most, then you’d look to the Moon. Maybe what you want most is someone who will take charge and get things done - then you’d look to Mars. Maybe you want someone who will uphold their end of the responsibilities in a relationship - you’d look to Saturn. Also, you would look at those planets through synastry and in each person’s natal chart.