Previously I prefer BHP but since they started the Contest to win Proton Inspira etc I found the quality dropped - I suspect they are using cheaper or inferior additives for RON 95 during the Contest season otherwise where they can get funds to organise such an "attractive" Contest.
For now my vote goes to Esso/Mobil as it give better FC (with power and no knocking)
Nevertheless Shell also give better FC but with less power and sometime there is knocking (especially) dirving up the slope.