AirPlay is a lot more stable than it used to be. You ask which is "better", that would be Bluetooth. However, I have a household where I have 4 different Bluetooth iOS devices to stream music from (and that's just me), plus wife, and children, all with iOS devices. Most Bluetooth audio devices (speakers) might store 1 or 2 pairings.
Bluetooth doesn't work in my house, because I have way too many devices and I'd have to ideally limit streaming to just a couple of them. AirPlay will work with any supported device on the local wifi network. I'm using Apple Airport Express as speaker hubs and any of the devices on the network can play to them. Other than that, I have the dropout issue maybe once per month at most. To me, the utility and flexibility make AirPlay superior.
Too bad also Apple is shutting down Airport production. That must mean AirPort will eventually go away as well. That will be a sad day and may encourage me to replace many of my iOS devices. Yes, Apple, really!