I am just in the middle of the same exercise, and have been trialling S/box, Airport, Linn, and Sonos. In my view it is down to your intended end users as the philosophies behind the systems are noticeably different.

Functionally they can all be similar - play most formats, from a drive or a NAS, include internet radio and local line-in sources, etc. It's clear to me that Sbox and Linn were designed by hardware engineers who added some control software, Sonos was designed by software and UI guys, and Apple is, well, Appley.

My end users are my family, not me, and they have a very low tech-gadget-config-pain threshold. So ease of use was paramount for my decision.

One major box difference is in the amps. I have in wall speakers so I need an amp in each room. That's included in Sonos and Linn but needs an extra thing for Sbox and Apple. Might not be an issue for you but for my kids it's one more thing to turn on / off / check.

The other differences are in the usage. Apple is designed to be best in an all Apple environment of course - I have a mixed set up so that wasn't the best for me. The SBox and Linn software is clearly engineering driven, with all sorts of 'click here to add in this module then reboot and alter parameters' stuff (the Linn is worse). I'm running off a NAS and at one point I got a "select which tarball to install" screen. Again, fine if you want to tinker and have complete flexibility, but not something I want to troubleshoot with my wife over the phone.

The Sonos unit is all about the control software design. You can't tinker with the boxes or setup - you only get what they decide to give you, but it has been by far the simplest to use and set up, and tech support so far has been "turn off, count to five, turn on"

So I have gone with Sonos. Hope that's useful.

Regards

Mark