As a Shell retiree I'm a bit biased. Switching brands supposedly is no big deal. I run Rotella T6 5W-40 but will probably switch to the new 15W-40. I live near Houston so cold start ups are not much an issue. I can't from your profile where you are but if you're in cold country you might stay with the 5W-40 unless you have a heated barn or a crankcase heater. Any of the name brand synthetics are good. I think Shell is using base oil from the Pearl Natural Gas to Liquids plant in Quatar. Good stuff.
If you really want to dig deep, look at:
https://www.bobistheoilguy.com/