I was big on Mobile 1 have been using it on 2 cars. For my newest car (2013 accord), I switched to Royal Purple. About the same price as the Mobile 1, but uses Class IV PAO.
I notice a difference. When my wife's car (use Mobile) calls for an oil change, after the oil change, I can "feel" and hear a difference in the engine. That tells my the mobile 1 oil is likely degrading more than it should between oil changes.
My accord (use royal purple) calls for an oil change about 9000 mile intervals. I change the oil and its like nothing has changed. I can't tell the difference between the old oil and the new oil.