If you have an Apple Card, then Exxon Mobil is the app and chain to use because it now features unlimited 3% daily cash back when you get fuel, convenience store, and car wash purchases -- in addition to building up points on Exxon Mobil's Rewards+ program, which gives you additional savings.
Exxon Mobil was the first app I tried to use for contactless fuel payments because I got a mailing direct from Apple Card at the end of June and was the inspiration for this piece. Overall, I think it is a very well-designed app from a UX standpoint, and the best of the three I tested. For Apple Card members, the app is preconfigured to use Apple Pay. There's no setup required, you just log in with your Apple ID and it's ready to use -- no keying in user account details, nothing.
You simply pull up to the pump, and the app automatically detects that you have arrived, presumably based on your GPS position. You can also use the app to navigate to the nearest Exxon or Mobil station using your preferred navigation app (Maps, Google Maps, or Waze).
Once you've arrived, the app prompts you to select the pump you've reached. There appears to be some intelligence or sensor at play here because it knew, for example, I was in proximity of pump #8, and it used a scroll selector to let me choose #8, #9, or #10. Once I selected the pump, there was perhaps a five-second delay before I was asked to begin fueling -- at this point, you select your grade of fuel at the pump and fuel away.
Once you're done, you hang up the pump, the app shows you your receipt, and you're on your way. If there's a data communications issue for some reason, you can pay with a QR code -- if the pump can display it -- but I haven't encountered any problems yet.