I'm going to say 370Z because it just looks more aggressive in all aspect - front, side and rear. But if you're a little older, you may like the styling of the Cayman. If I ask this question to a 23 year old, he will instantly pick the Z. But if same question asked to a 31 year old male, he may pick the Cayman. I wish Z had the (sports pack) rear spoiler. I feel that makes the Z look better.
He says it at 3:49 "Porsche looks a bit girly"