3.6 if you want to make 7 to 8 lbs of boost with headers. If no headers, then the 3.8 will make about the same boost.
You have headers don't you? I do. That's why I went with the 3.6" pulley. If you look at my dyno sheet, you can see the boost varied between 7 and 8 and my car made 500 rwhp.
Still nice and safe for the engine internals, but oh so fun.