the way that sonos allowed you to synch or separate music (play the same or different things on your different devices) used to give it an edge over squeezebox, but that all got updated last year, so now there is no difference in functionality.
now that the ‘boom’ has been discontinued and the ‘receiver’ is hard to get hold of, sonos gives you more options for built in speakers, or small devices with no interface on them. I’d probably agree that sonos looks better too.
For me though, squeezebox does everything I want, uses the network and NAS I already had and has a really intuitive interface.
Dave