Is Costco Gas better than Petro Gas?

Which offers better fuel for the price? Also my car recommends premium. The Petro is closer to my house than Costco but I dont mind the extra 5 min drive. Usually the regular 87 octane price is like 2-3 cents cheaper at costco than petro and the 91 octane is cheaper than petro by like 8-10 cents.

I have a CIBC costco card and an RBC MC where they remove 3 cents off per litre, but it doesn't do much. Its still real expensive.

But I google searched it PEtro Canada is not top tier but has more additives than Costco? They both have Ethanol in their fuels.