I can't speak for the Companion 3 or 5's, but would recommend against the Companion 2 speakers. I bought a set, which sounded great in the store with the company setup and selected music. But when I got them home, they just didn't sound right. I went back to the store and bought a set of M-Audio StudioPro 3 audio monitors and the difference was night and day. The M-Audio speakers produced a much more accurate sound with an amazing midrange that is all but lost on most other computer speakers. To be honest, I can't imagine the 3 and 5 series would be much better. Whenever you have these setups with tiny satellite speakers and a big subwoofer, you get boomy base, tinny acoustics and no midrange.
If you really care about the sound of your music and don't listen to a lot of hip-hop, go with something like the M-Audio speakers. If you just want something that looks flash that matches your computer well and you're easily impressed by big thumpy base, go with the Bose sets.