There are plenty of bluetooth enabled speakers avalailable on the market. It depends more on the other use cases (outdoor, indoor, sound quality, fixed or movable) which speaker is the best solution for you.
Also there are plenty of speakers now available with built in WLAN capabilities.
Outdoor use case
For going outdoor you should select speakers that can handle water, like e.g. the Sony SRS-XB31.
Also setting up a WLAN including a router and connecting the speakers is not so easy to handle.
In this case it maybe makes more sense to restrict oneself to a bluetooth party chain solution only. This is some offering by Sony.
Upgrading an existing environment
Some people, of course, have an already existing environment and want to upgrade or extend it.
A very good description how this can be done is given by Euronics.
A very good overview for commercial and complete proprietary solutions is given by Conrad.
If you are fine with using the Mac or a windows machine as a server, Airfoil is a quite nice solution. You can stream any application running on your server synchronously to plenty of devices, including multiple bluetooth devices.
I’m going for the max2play solution now. Yes, it’s more costly as you have to have multiple Raspberry clients running. But you are more flexible as well. And it makes more fun playing around with the Raspis 😉
Use of Rpi output or USB soundcard or expensive DAC to connect to the speaker
Play different music in different rooms
Control it remotely, also via an app like squeezer
Don’t need a Windows or Mac as a server
Cannot connect to multiple bluetooth devices with one RPi