I've driven the 370z and thought it was pretty nice but felt like the S2000 was more enjoyble to drive
Personally, I would chose the 370z with sport pack vice the NISMO but if I had the funds I would get a 10' Porsche Cayman S in a heart beat.
The 2010 Porsche Cayman S is faster than both (straight line /track, it doesn't)
Porsche Cayman S vs. 370z
Nissan 370Z vs Porsche Cayman S(facelift) PDK - FastestLaps.com
Porsche Cayman S vs. 370z Nismo
Porsche Cayman S(facelift) PDK vs Nissan Nismo 370Z - FastestLaps.com
This new Cayman S is more comparable to the E92 M3; it’s in a different league al together. The Z is good for the money though