There are very few sources for motor oil. Those few manufacturers make oils sold under different names.
As far as Mobil 1, they have different synthetic oils. The EP is much, much better than the original Mobil 1, and I use it in my Yamaha outboard. I previously ran Rotella in my outboard, and it's great (for the price) for any vehicle or boat that doesn't have a catalytic converter.
I'm running WallyWorld's house brand full synthetic in my cars. It's made by Exxon/Mobil. And it's about the same price as everyone else's dino oil.
If you have time, look at BobIsTheOilGuy.com. It's the comprehensive website/blog about anything to do with lubrication.