I'm using Vpower and apart from the first fill of Tesco 99, it's had nothing but. A few reasons:
a) The Shell garage round is just round the corner from me and they are pretty cheap for my area
b) There is not much in it price wise between that and the 95 ron they sell
c) I've picked a Drivers point card and you get double points on Vpower (lol yes I'm sucker for stupid loyalty points schemes - so get money off vouchers back)
d) Maybe the most importantly - I had assumed it would perform better in my car and keep it running cleaner/more efficient, so would get the best out my engine.
Even it the test results aren't that scientific they look promising and it the right direction