I spent quite a bit of time comparing the two and finally selected the Companion 5 model myself. Now I grant you I am a big Bose fan (after getting my first pair of Bose 901s in college), but I still feel these are the best sounding computer speakers I have yet to hear.
I moved up to these from a set of Harmon Kardon Soundsticks II which I liked pretty well and the main difference in these is the simulation of surround sound that is surprisingly accurate. It does indeed seem that the sound field is extended far beyond what you might think possible for two SMALL speakers and a subwoofer!
If you get some (be it the 3s or 5s), just make sure you first select them in the "Speakers" pane in your System Preferences. Select "Output" then select "Bose USB Audio". THEN go into "Audio Midi Setup" in your Utilities folder. Use "Configure Speakers" to select the "Multichannel" tab, then "5.1 Surround" in the drop down list to enable the full surround simulation. Makes a HUGE difference!
Anyhow, yes the price on the 5s was painful for a set of computer speakers, but that pain only lasts for a short time when you are watching a good movie or enjoying some quality music! I don't regret buying them at all- plus the "hockey puck" volume adjuster/audio input device is cool too!