Shell Petrol is comparatively better than PSO. To me it seems that most of the PSO outlets mixed unbranded petrol with the company provided one.
However PSO outlets with 'Company Maintained' logo does not have this thing and are better.
But still Shell Petrol is better than PSO, Total, Caltex and others.
I think they have better RONs then their competitors.
And yes, this "Techron technology" thing in Caltex Petrol is a scam in my opinion, the additive does not effect a single thing.
At the end of the day, which station you fill up from, matters the most.