i have not driven either cars but for me, i'd go for the 350z.
the evo8 is living proof how good you can make a 4door sedan. looking at the components alone, i think it is a very value for money proposition. i know because i drive a normal 4door sedan and if you were to do the sum of not just buying and installing, but engineering the following to work well as a complete package-turbocharger, oil cooler, intercooler(even basic cooling from radiator), brakes, suspension, flared arches, bodykit, recaro seats, 4wd transmission with the multiple LSD's, AYC, rims and tyres and more, then you will see that the evo8 is in fact very cheap for what you get. try to spec up a normal lancer to evo spec with brand new parts and it'll cost way more. i really think there is a lot of assets on it straight from the factory for a reasonable asking price.
the evo8 is also a very practical car since its a 4door sedan.
the evo8 flatters any drivers due to the genius in its handling. it doesn't take a very good driver to get a very decent lap time.
the evo8 is perfect on paper. period.
but the evo8 is not a grand tourer(GT) and certainly not a sports car. it is a car in sync with the modern world of instant noodles, 3in1 coffee sachets, quick shags, quartz digital watches etc. it does what it seeks out to do with ruthless efficiency. it is instant gratification.
the 350z on the other hand, in comparison, is the car parallel of old fashioned approach of making noodles fresh from scratch, coffee ground straight from the bean and espressoed with pressure, a deep and meaningful relationship in a temporary world, and a carefully handcrafted watch with a tourbillon mechanism.
it doesn't look too shabby either on paper-individual throttle bodies on a 6 cylinder(albeit V) engine(today, the only other place you get that is on the m3 and rb26), brembo's all round, double wishbone front and multi-link rear suspension(the ideal layout for a sports car), rwd(the driving enthusiast's choice), naturally aspirated biggish cc(the purists' choice).
where the evo8 will flatter you all the time even if you can't really drive, the 350z penalises you for that and rewards you accordingly when you have improved. i think its a good platform to learn how to drive.
but the most important point to me, i feel, is that the 350z has more passion. it has that inexplicable emotional factor that just makes you feel different. its pure and simple. of course it doesn't have the passion of them italians, but whatever i say here is in comparison to the evo8.
so, the 2 cars aims to provide driving pleasure but took diametrically opposed approaches. though i feel the evo8 started off with a compromised platform compared to the 350z, driving pleasure wise.
but everyone is different. this is my opinion, and why i feel so. i only wished i could confirm my opinions by owning both to know them deeply.