I'm all on my own here, but I've voted for Hightower. I really like her relationship with Patrick, because I think it works on many levels. For example, I love that she felt comfortable giving him advice about his love life - I don't think anyone else could have said what she did. She's strong and smart, and Patrick has to be at his best to outwit her. But she also can't help but be charmed and amused by him, and knowing that, he uses it to his advantage. As a result I think we've seen some wonderful moments - "I do love to dance" and the kiss on the cheek are 2 examples that spring to mind.
I did also consider Leroche, because I think he's a great character and I always enjoy his scenes with Patrick. But I decided that he's a little too dark and so I think he works better as an outsider.