They've both got good looks but it depends on your idea of what a sports car should look like I think. I agree with Ekona and his comments. For me its the 350 (HR), the older models are touching aged with the lights and minor bumper tweeks and if they have those curvy rays.... a sports car (to me anyway) should have some sort of length to it, be wide...or wide in appearance and be low (i dont mean modified slammed low though..thats just vile lol). The 350 has a bit of a tail at the back which the 370 doesn't so it makes (the 350) look less 'stumpy'. Stumpy heads towards that mini-hair dresser look that a TT has. The 370 has a bit of that but its wide appearance looks great front or back (especially having recently seen G-Mans Nismo infront of me ). Even simple touches like the gold calipers on the 350 as there not flat its a flecked kinda metallic in colour and when clean look great against the sharp rays. I agree the rear of the 350 is a bit iffy but still looks good from the back, low squat stance that it has, just not as much as the 370. Interior wise better quality 370, but design wise, with its cascading dash the 350Z with the metal bits looks better in shape, with the wrap-around doors meeting the dash etc.
The best by far though is the new style 370Z Nismo, spot on with that.