Very well matched so in theory it's a tough call.
Samantha looks as if she might be quite sweet so I see her as the good girl. I'll cast her as the girlfriend.
Anna look like a bit of a bad ass so definitely the bad girl for me. I'll call her the ex who has lost her man to lovely Samantha. And of course her ex-man offers her the chance to get back together. She just has to make Samantha submit in a vicious catfight.
Anna confronts Samantha in front of the (lucky) man, verbally abuses Samantha then grabs two handfuls of her hair, gets her down on the ground. There's a lot of rolling around, hairpulling (both) and scratching (only Anna to Samantha).
Anna mauls Samantha but Samantha refuses to submit. She won't lose her man to the bitch Anna.