I normally user purolator Pure 1 filters and whatever syn I can get cheap.
Right now its pennzoil platinum that I got for 1.99/qt
Next couple times its going to be valvoline maxlife syn 5w30. I got for 35cents/qt
Pretty much any sm rated oil is ok but I normally avoid COASTAL as they have been
found to be out of grade in the past. Also avoid anything that says non detergent
or for cars older than 1988.
While it is true there are only 3 or so refiners the additive packages can vary wildly
by brand. For instance valvoline ALL Climate is pretty anemic with their additive package.
And valvoline max-life has a much more robust package.