Based on what I've read and what I've learned from others that have tackled this question:
-12AN if you plan to track the car a lot.
-10AN is usually plenty for casual street driving and the occasional spirited run or two.
In colder climates, the
oil cooler is often overkill and doesn't allow the
oil to reach the proper operating temperature. I have to use a block-off plate on mine during the winter, even here in So Cal.
-Dean