Not brand loyal here.
My car (2003 Saturn ION) would frequently get Q-Torque 5w30 because it was $3 per quart. Later, PP was sold at $3 per quart, so I bought loads of that. the most recent batch of oil was from 2 years ago, Vavloline synpower 5w30 at $2.55 per quart. Before those bargains existed, I got M1 or WM synthetic.
My mom's car (2005 Jeep GC) originally called for 5w30, so I filled it with M1, until Q-torque 5w30 was sold for $3 per quart. I later found 5w20 Q-Torque for $1 per quart, so I used it. Currently, I use RP 5w20, because I bought tons of it at $3.50 per quart.
My father is brand loyal. He only uses M1. He used M1 5w30 until M1 AFE 0w30 came out. Now he only uses M1 0w30.
This could get even more complex when power steering fluid, transmission fluid, and those other oils that don't go into the engine.