What’s your reason for getting it? Is it just to use for Text-to-Speech purposes with ST? If so, then I’d say go with cheaper. But if you also want music Sonos is more established and probably better interfaces will all the streaming options out there.
BUT… you also have another possible option depending on your level of technical know how. Echo, in my opinion, does a very nice job of playing music. I don’t have a Sonos so I can’t compare, but I’m honestly blown away with the quality of the speaker. Obviously Echo doesn’t do any TTS yet, but there are ways to fake it.
If you have an old Android tablet or phone you can use DLNA software to make along with some smart apps to mimic a TTS capable speaker. Then, bluetooth that device to Echo and now you have TTS thru Echo (kinda). That’s what I did recently.
There’s another side benefit of doing it this way as well. The software that @ule wrote includes the ability to use an outside TTS processor. Given that the SmartThings current TTS functionality is flaky at best, this provides a reliable backup for the SmartThings “built-in” method.
It’s certainly another option, but there really is no comparison in sound quality. Even the Sonos Play 1 will blow the Echo out of the water in terms of audio quality. I have both, and each has it’s place. I wish I could talk to my Sonos speakers, and I wish my Echo sounded as good
If you want something simply for alerts and notifications then I would recommend looking into @NWTony 's upcoming TTS notification app that is rock solid and reliable (doesn’t rely on SmartThings problematic TTS in the cloud) but rather his own TTS directly on an inexpensive Android phone or tablet.
I have the echo already I was looking for music for the bathroom. Alarm clock if possible. Or other places since it is portable and Bluetooth. I liked the idea that sono can make sounds like when you get home. I have tons of questions like using my DSC wired home alarm with ST. Not sure if that is possible. Like I said still reading and learning. Also would like to know about RPI with echo / ST.