To be honest....... It doesn't matter.
I've spent plenty of time and money on this topic but the truth is most oils are great. And I do mean that.
Shell is great, Havoline is great, Castrol is great, Total is great, they are all great.
The differences between these will only appear under very high stress circumstances towards the limit of their operating conditions.
As long as you are replacing your oil at the correct interval with "genuine" oil of the correct grade and you don't use your car in a very specific manner, you're all good and you will most probably never feel the difference.
If you're car is running well on Castrol, stick with it.
Stories of a 15% decrease in fuel consumption or a much better throttle feel after shifting from Zic to Total for example are almost entirely fictious.
