i do like Mobile 1 but Valvoline is right up there with Mobile 1 on my list, in fact Valvoline in my opinion is about up to par with Mobile one as one of my favorite oils and my old Buick Century Custom loved both! there is a reason why Ford chooses or chose Valvoline, its a good oil! a guy i worked with when i was a mechanic swore buy ashland which i hoped i spelled that correctly is the company who makes the oil for Valvoline and NAPA oil which is in fact the same thing! so keep that in mind when shopping for oil, NAPA oil is pretty much Valvoline oil!
as far as Royal Purple, as soon as barneyb stated something about Amsoil i have been all over that with research and some tests show its a better oil, been all over car forum posts, they say its better than Royal purple, weither it is or not don’t know i don’t race cars though i wish i could. and if the phrase you get what you pay for has any meaning its according too there website about $11.00 a quart, while Royal purple is about $9.00 a quart, so maybe i will try some Amsoil my next oil change if i can get anywhere that sells it!
now this begs again the question is it worth buying, sure if you want too, but in my honest opinion a daily driver you will do just fine with what the manufacturer recommends, your grade and vescocity of oil, whatever brand you want, Mobile 1, Valvoline, Castrol, don’t care whatever you like, keep it changed and clean, check it every week or so and that is what keeps a engine happiest! there is no miracles too be had with Royal Purple honestly though its good oil and has a strong film strength its not a miracle oil.