You hit the nail right on the head there, instead of asking us which car is better you should be sticking ur a$$ in a couple and driving them after all you the one you is purchasing the car and if u cant fit in the S15 coz of your height then ur only option is the 34 or another larger import.
I found the S15 to be very agile and very easy to throw around where as the 34 is a lil more solid as with most skyline's coz of there size and weight, both are great cars.
However the NEO motors are not as good as previous RB's
hope that helped