The Sonos system basically creates its own wireless network (you will have to also buy a Sonos:Bridge although many places are giving those away now with other Sonos purchases), so you can access it anywhere you have wifi access. You can buy a Sonos Connect:Amp if you don't want to have to connect a separate amp to the Sonos system. It's obviously pricier (around $500) but it is also small and compact if that is an issue for you. I'm a fan of Sonos because it is extremely easy-to-use, regardless of your level of comfort with A/V systems or "universal" remotes, and it's compatible with iTunes, Spotify, Pandora, etc. It is expensive, no question, especially if you start adding a lot of components. One thing that is nice is that it gives you the ability to later add wirless speakers to the system if you have an area where you didn't hardwire connections initially (I have a Play:3 in my garage).
Airport express is great, but obviously it also requires a separate amp. You can send anything you want to it if you have an iOS device via Airplay, which makes it also pretty easy to use. It also becomes part of your home wifi network, so range matches your wifi.