I typically go for whatever is cheapest. The cost of gas is getting too insane for me to do otherwise. It's currently sitting at $1.43 a liter. If all the prices are equal, then I'll usually stop at Shell or Petro-Canada as both have decent reward programs.
Most United or Coles (Shell) stations..the cost generally determines and these 2 places are winners.
En route to Geelong however I like the BP place because they have some good food outlets and people selling fruits/other small items at nominal costs. We usually stop there for breakfast/brunch + fruits before we carry on to Geelong/beyond for long drives.