Damon is my top fave. Followed by Vex, June, and Cal. I really developed a soft spot for Cal thanks to the Valentine dlc. Also, throw some love to Seb as well. xD
But honestly, I love all the boys. I like the girls to, but I've no interest in romancing the women. Ayame though is my best gal friend. ^_^
Basically, I have a save for each of the boys. I mostly play as a Tilaari, though my character for Seb is a Kitalphan. So he can haz his mermaid. xD