If you want the very best, NEO synthetic oil is the go. It's the only oil the public can buy which is derived from a fully synthetic diester. Their gear oil is specified by Hewland. Club racers & motorsport pro's use this stuff. Amsoil is also very good. It used to be derived from a full synthetic diester, but they changed the recipe. Then you've got your regular oil companies (Shell, Castrol, Mobil etc).
Nissan specify 7.5w-50 or 40 (can't remember which) in the Jap owner manual. Don't use cheap sh1t oil...