90% of the time I use Shell, based on: station proximity, Formula 1 sponsorship, having their EasyPay tag, their gas being Top Tier and I find the stations neat and clean.
Petro Can and Sunoco are the backups. I try to avoid Esso at nearly all costs based on how filthy their gas is (or perhap was when it had nearly quadruple the sulfur of other brands a few years ago).