Oh goody.....another "best" oil question. Here we go again....
This falls into the same category as "Best":
Tyres
Cleaning fluid
Wax (some get really upset if you even dare to call it "polish").
Petrol (some get VERY upset if you call it "Super", not "V-Power").
and if you're into cars,
Antifreeze... sorry, mustn't call it that - COOLANT.
I've tried both the recommended engine oil and ATF - it didn't seem to make much difference overall but the only time I suffered a cooked clutch was off road when using ATF.
Built like a gun... could go BANG!