Airplay is very compressed , but even mconnect upnp app on apple devices is poorer quality than say bubble upnp on android as the signal gets processed via the apple device rather than handed off directly to the streamer ( but it's still way better than airplay.
A streamer is going to give you a good lift in SQ.
100% avoid power line networks you do not want that noise in your mains.
Wi-Fi can be excellent if you have good coverage in your property but quite a few folks including myself find hard wiring Ethernet to be better , however I've got optical isolation and an Etherregen between my router and my stereo.
If you want to keep it simple and lower budget wifi is a good option and may well be better than Ethernet cable directly from router to streamer.
Get a good broadband bandwidth for the best experience with fewer dropouts.
good luck