For me it’s Siri being processed on-device. This is a game-changer on iOS, because 30-40% of the time, my Siri requests would be met with her being unable to process what I want since she cannot connect to the internet for some reason. Now when I’m in the gym and I have a weak data connection, I can still ask Siri in my AirPods to control my music, since it’s all processed locally, and almost instantaneously.
This also extends to voice-to-text, which is far more reliable and quicker now. I can only hope that one day on-device Siri processing comes to the Apple Watch and HomePod/Mini.
The runner-up would be being able to pop into voice messages sent via iMessage, and scroll/seek through them. The most annoying thing for me is getting a voice message that’s on the longer side, having it interrupted, and having to start back from scratch. Huge waste of time! We still can’t background voice messages when they’re playing, but at least we can seek through them now.
These are two smaller quality-of-life improvements, but they make the overall experience so much better for me.