I rotate my G6 between my upper outer arm, upper inner arm (so it's facing my ribs when my arm is down at my sides) and my outer forearm (so if I hug my body with the sensor arm, the sensor would be facing out).
I rotate left and right side, and (with the G6) place the round side of the sensor aimed out toward my hand for one rotation, then facing in toward my shoulder for one rotation. It's probably unnecessary, but it doesn't hurt anything and varies the exact site of the filament a bit.
Outer forearm is definitely my favourite spot - I get the best readings, it's less prone to getting bumped (because I can see it), it doesn't lose contact with my pump and phone, and the adhesive stays in the best condition compared to the other two spots.
Outer forearm is not approved by Dexcom as far as I know, so I don't expect replacements, but I've never had issues with any of my Dexcom sensors in this spot so that's not something I'm worried about.