It's a tough call, but I'm going to say Scarlett Johansson.
If you're just going by looks, I'd say there are plenty of nominees, but I'd pick Scarlett because she just seems like she'd be fun to hang out with too.
Actually come to think of it, so does Mila Kunis...
Ok, so Scarlett Johansson AND Mila Kunis. I've spent a grand total of 0 seconds in their company, so it's hard for me to know for sure... But they just give off a vibe like they'd have a good sense of humour and wouldn't take themselves too seriously.
Although, if you're going on looks alone - I might change my vote and go for Megan Fox. And Jessica Alba is pretty stunning too! They both look like they'd be high-maintenance, but some guys like the challenge I guess.
I also thought Amber Heard was really hot in The Rum Diary, so maybe if she was in town I wouldn't mind going to Nandos with her or something like that...