Test one: Streaming
This should be easy in theory. Create a Shared Folder on your Mac or plug in a uPNP-able NAS, and go. But in practice, it can be fiddly.
Apple TV is by far the easiest to hook up to your Mac, plugging straight into iTunes, though it's heavily limited by the fact that iTunes can barely handle any formats at all.
For the others, you usually get the smoothest ride with a dedicated NAS, or running a uPnP client instead of relying on OS X. Aside from Apple TV, most support all the main media formats you're likely to have around, including most of those floating around the internet.
You typically select them from file-based lists of Music, Video and Photos, although the Boxee Box and PopBox try to identify your files and present them in a more structured order - seasons, episodes, cover art and so on. Unfortunately, in practice Boxee failed miserably at identification, while the PopBox missed even the existence of many files.
Test two: New content
The Apple TV is the only one of this set that offers proper movies and shows, obviously via the iTunes Store. If you buy a lot from there, no problem.
Further afield, you're out of luck. Of the others, Boxee has the best range of online content, including the BBC iPlayer. The catch is that not all of it is guaranteed to play, and the way it categorises its collection leaves much to be desired. A movie about Hitler's bunker heading up Comedy? A dodgy-sounding Japanese film in Animation? Okay...
The others offer a mix of content. Almost all - even Apple TV - offer YouTube and Flickr, though neither iPlayer nor web shows are yet guaranteed. Only Boxee and Apple TV (if you're willing to pay) feel like devices you'd sit down in front to see what's new, which is a shame.
In almost every case, you're limited to what can be streamed for free over the web, and there's no guarantee that your device's Flash player will ever be updated.
Test three: Ease of use
Every media streamer here is very similar. Take it out of the box, plug in the HDMI cable (the PopBox also supports component or composite), Ethernet cable or wireless dongle and plug it in, and only punching in your internet settings should be left.
Apple TV is by far the easiest to get running on your network, thanks to iTunes Sharing. With the exception of the PopBox (which took much fiddling) none had any trouble connecting to our NAS either.
Mac-based sharing was a different story, with lots of error messages and cases where the streamers would see our test Mac but not actually be able to connect to it. A UPnP server is usually your friend here, but an added point of failure: none offer much, if anything, in the way of manual-based help.
With everything running, you're left with simple menus. The Boxee and Iomega win bonus points for their keyboard/remote control hybrids. Otherwise, there's little in it to separate them.
Test four: Interface
For pure sleekness, nothing beats the Apple TV. It doesn't do anything like as much as the others, but what it does, it does beautifully.
Boxee too stands out, with its heavy use of images and transitions between its own interface and services like iPlayer; we also liked options such as being able to prioritise your own content over web-based content.
The only downside is that often, you're not getting as much as it looks like - a single episode of a show via Five's catch-up service being displayed as if it was a full series to sink into. It's disappointing when you're busy virtually channel-hopping.
The other streamers are all solid but unexceptional lookers - no interfaces that you'd be ashamed to have on your screen when guests are around, but with little that makes them more than the glorified Finders they basically are. The PopBox is rough and black, the WDTV Live colourful and chunky. The others land somewhere in the middle.
The best media streamer for Mac is: PopBox
If all your content is in iTunes-friendly form or bought from the iTunes Store, you really can't go wrong with the Apple TV. For most users though, it's just going to be too limited.
Elsewhere, in terms of pure features, the Boxee Box would easily take the prize if it hadn't spent much of our test time falling on its face with goofs like insisting an old TV episode was the movie Salt…
Having said that, it's still by far the best performer for web-based content. Unfortunately the cost of the Boxee still brings it down a peg or two.
That leaves the PopBox as the best all-round media streamer in our test - it offers iPlayer and other web content, good categorisation and a wide range of extra features. But be warned: the catch is that it can be a real pain to get running on first attempt.
If you're not comfortable getting your hands dirty, don't rule out the Apple TV or WDTV Live Hub. We're confident either of those two will get you going much faster.