XANATOS has the best marriage proposal ever in canon and by best marriage proposal I mean he is as romantic as a bag of rocks. "Marry me. We're genetically compatible, highly intelligent and have the same goals. It makes perfect sense to get married. ... I think we'll love each other. As much as two people like ourselves are capable of that emotion." THIS PRETTY MUCH TELLS YOU WHAT HE WANTS IN A WOMAN. She needs to be crafty, smart, and just as ruthless as he is. He doesn't care about looks, as you can tell by him marrying Fox, a woman with a hugeass blue tattoo on her face.
(and, despite all his bluster about 'I don't love Fox, I'm above love, you found my weakness Goliath it's love', he really does love and care for Fox in canon. He just doesn't want to admit that he cares about people. :< )

KLARION thinks girls have cooties. Like, he super wigged out when he got kissed, so he's not gonna be finding anybody attractive any time soon.

CONNORS is from the one alternate reality in a billion where he isn't married with children. Anyway, from what we know about Martha Connors, she's compassionate, a good wife and mother and, depending on the adaptation, is just as good as he is in science. With all of Connors' issues about his arm though, he probably isn't looking for anybody to date at the moment and dating is at the back of his mind. If asked, he'll probably just respond something along the lines of 'well she should be smart and caring, please pass that test tube'