I'm loyal to Valvoline and all of their products.
This started for me back in 1987 when I started driving. I am a fan of Mark Martin, who used to drive the #6 Valvoline Ford. The sponsorship worked for me.. although he runs pennzoil on his #5 car, I'm still stuck on Valvoline.
For my own vehicles, I'm at 75% valvoline products. 10% redline and the rest everything else. (namely MMO and Seafoam).
For relatives and friends, it's kindof a tossup. Usually Mobil 1 for some, mobil clean 5000/7500, Castrol for my neighbor, my other neighbor who has a 94 civic that needs to be retired, I use my recycled oil droplets (I have the bottle funnel that takes the oil drops left and drips it into another bottle). So that's a hodge podge, if I don't have any, I buy the cheap autozone valucraft oil. But I usually have enough of something lying around for her car.
I don't skimp on filters though.. Wix all the way.