As Briggsy has said if you go for the Eibach springs you will need camber correction so if you don't want the expense then the Teins would be the way to go but the alignment will still need done once you fit either.
We stock both options,
http://www.350z-uk.com/topic/78817-tein-s-tech-springs-in-stock-for-350z-17350-delivered/
http://www.350z-uk.com/topic/78673-eibach-pro-spring-kit-350z-23750/