Honestly, I wish I could use Android Pay. My phone is a Moto G4 Play so it doesn't have NFC capability. The airline app is probably the safest bet for boarding passes since you want them to WORK and have usable bar or QR codes.
Now, what I couldn't figure out last time I traveled was how to get both my boarding pass and my son's to show up on the American Airlines app. I was able to check us both in, but only my pass would display so we had to print one for him. He's under 18, btw.