I'd say Spec-V If you don't plan on modding too much then the potential of the wrx doesn't really justify it. I have encountered two Spec-V's in my time with my wrx. Both of those time I was stock and the spec had like a cat-back and maybe intake. from a roll I would edge them out by only a small margin. as far as handeling stock for stock I'd give it to the spec-V again. the only other japanese production car sold in the US to have a helical LSD was when Acura brought over the Teg TypeR. they are lighter and have great low end torque if auto-x is your thing you will be very happy with it.
If you were going to mod and possibly Rally I would tell you differently but for what you have put out. I would go with the Nissan.
good luck with whatever you go with.