we're quite happy with the M35 series 1, but thats got a few mods, and it moves along pretty quickly.
i think the vq35 would be an easier car to drive, as ours has a little bit of lag, but when boost hits, it hits.
wife doesnt mind the seats in ours, but i think there's room for improvement.
i'd agree with ppl that say if you're modding, go the s1, otherwise the s2 is a more balanced car.