I'm going to assume we're all familiar with the 350Z, have all owned/own one, driven one and of course seen one in the flesh. The problem with this argument is you're putting an 8 year old design up against a current 2 or so year old design. A lot of people seem to disagree with this in the past but the turning point for the 350Z in my mind was the facelift. I personally prefer the facelift to the original 350Z, the tweaks worked so well. The lights were far better and the bonnet for me was so nice, it finally gave the 350 the much needed muscle car presence. I have to say I loved my facelift 350Z.
Now moving onto the 370Z it's completely different. I must admit, like others, when I first saw pictures of it I didn't like it all that much. Then I saw one in the flesh and I have to say I was blown away. The 370 never made me think any less of my 350 though and I love the 350 just as much as I always did.
In short, you really can't say which one you prefer. They are different cars in their own rights. Of course the 350 owners will say the 350 is better looking at the 370 owners will say the 370 is better looking, one things for sure they're both future classics with regards to the cars and their shapes. I'd find it hard to say which is the better looking.