If Duncan will not win due to his criminal activities, then I doubt Harold will either. They wouldn't want to promote cheating someone else off. Here's who I'm looking at.
Leshawna: Doubtful since she hasn't been doing much of note, although she could pull an Owen.
Owen: Doubtful because he has already won
Lindsay: Doubtful because she's not lovable or determined enough. Her "leadership" role didn't last long enough to give her endearing qualities.
Beth: Doubtful because she hasn't done much. Seriously, all she's done is try to be friends with everyone and still act delusional.
Duncan: He's mellowed out, so he could take the prize home.
Harold: I doubt it considering Courtney's return.
Heather: Doubtful, they don't let villains win
Justin: Ditto
Courtney: Doubtful because she enters in mid-season
Izzy: Doubtful because she's already been voted out. Twice.
A lot does hinge on Courtney's return. Duncan could fly high or go home with her around, and I doubt Harold will be pleased to see her, although there's a chance he'll redeem himself with her. It also gives Courtney herself a chance to redeem herself.
Remember that between Owen and Gwen, Owen was a better, friendly person then Gwen is. It helps to compare characters directly.