Hey welcome aboard.
My best advice is to just test drive both and see which one you like better.
The nismo aero is functional and to duplicate it with aftermarket body pieces, wings etc that match up to the car and look/fit as good as OEM will be pricey.
However, if you don't like the way the nismo looks compared to the base/sport pkg Z then obviously go with the non nismo.
Powerwise, the nismo has a slight edge but the two really begin to even out once you start modding.
In sum, just get the one that makes you happiest and enjoy it.
