In my opinion - Quaker State 10W40 or 10W30.
I know it's not the popular choice but I'm getting exteme life on my engines with Quaker State. My Triumph GT6 for example was purchased new in 1972. After 29 years of ownership including 5 years of autocrossing and over 210,000 total miles the engine still runs like a champ and has never been opened for internal service. When I adjust the valves the valve train is clean with nominal wear for the age of the vehicle. Another example is my 1986 TransAm. Purchased new 15 Years Ago - 165,000 miles on the ticker and just starting to do the classic Chevy cold startup - small puff of blue smoke routine. I'm getting ready to fireup a freshly built 403 Ford FE in my 427SC. It's carrying 9 qurts of 10W40. For me it's 3000 mile filter/
oil changes with Quaker State and no problems expected.