Katherine the most. She's psychotic! But also Caroline, and I can see Bonnie being over protective. Elena..not so much w/ Stefan. Maybe that will change when she gets what she really wants ;]

Caroline and Bonnie I think. Katherine just flat out doesn't care, but then again, she would probably see the person as hers. So maybe she would be really possessive. I don't know. She's too insane to really understand.

Katherine said it herself, she's spoiled and selfish so she'd def have the most potential to become a crazy/possesive gf. I think she would see the guy as her property. I felt that vibe from her a few times with Damon + Stefan, that they were hers.
I could see it a bit in Caroline too but not as bad as it would be with Katherine.

Isn't she already? :D
Maybe Caroline too...

Both Katherine and Caroline. Katherine likes to be in power and control, whereas Caroline is very insecure.

Katherine, Caroline, and Bonnie.

& Katherine.