Shell or Chevron 91 octane only. Once had to put cheap grocery store 91 in the R50 and it ran like garbage for a month. Because of that experience I try and avoid anything else.
Cheapest i can find but ever so often treat eg six monthly it to shell v powernitro. Can never tell any difference and our direct injrction engines cannot benefit from valve cleaning etc these fuels advertise but i suppose they could help fuel system and eg injectors cylinders!
I always use Sainsbury's 97 Super unleaded as decent price and get Nectar points. Probably nothing factual behind this but I always choose a fuel supplier and stick with it so the ECU has a constant factor rather than a variety of different fuels.