I will start by saying that I am a huge Sonos fan, but also a huge Apple fan. In addition to a multi-zone Sonos system, I also use AirPlay within my house for various uses, so am quite familiar with both. Whenever Sonos comes up on this board there is a ton of disagreement and often misconception.
1) Both Sonos and AirPlay are options to wirelessly stream to speakers. They accomplish it in somewhat different ways, and there are certain capabilities/features/options that are unique to each. In fact, there are methods of integrating use of both Sonos and AirPlay within existing home speaker/AV setups as well as configuring purely stand-alone solutions. Both are very flexible and can cost from a couple of hundred dollars to many thousands of dollars.
2) Both Sonos and AirPlay are proprietary systems with various levels of integration with outside providers/services. Neither is completely open and this fact often becomes the source of debate on which is better. (Side note: It is ironic that on an Apple board people complain about a walled garden approach.)
3) Sound quality and cost is very subjective. I've heard people describe $30 bluetooth speakers as offering amazing sound, and there are others that would spend $10,000+ on a pair of floor standing speakers without hesitation to achieve the quality they'd desire.
4) Ease of use is also very subjective. I personally find both Sonos and AirPlay options easy to use, with Sonos being more "centralized" because Sonos requires that all content is played via their app, simple as that (unless you experiment with the unsupported AirSonos). AirPlay can be triggered from multiple apps, iTunes, from OS X, or from the iOS control center, so while more points of origin, it also can be considered more confusing. (Side note: I bought my very very tech challenged dad a Sonos Play:1 for Father's Day, installed the app on his iPad, and showed him in about 60 seconds how to use it. He's not called me once for help.)
5) The Sonos app is available for multiple platforms, including iOS, Android, OS X, and Windows. AirPlay is not cross-platform (there may be options to use AirPlay outside of Apple devices and operating systems, but I am not sure about such capabilities).
So is one better than the other? Not really, and it depends on many factors and preferences. If you are looking for a streaming solution, I'd encourage you to evaluate both and see what best fits your current hardware, software, services (such as Spotify and Apple Music), etc.
Also, if you have not actually used Sonos, particularly in a multi-zone setup and not just at a Best Buy, then simply comparing the features to AirPlay is not giving you the full flavor of the functionality and ease of use.