go with the computer version. I've had both.
The computer version (XM PCR ~$50) displays all the songs currently playing on every channel.
It also has cool features like the ability to save favorite songs and artists and then notify you when that artist or song is playing on another channel.
One problem is that the XM PCR comes with a directional antenna that (in most areas) wont get good reception in a mobile enviroment. To overcome this problem I used the XM omnidirectional antenna that came with my stand-alone Delphi unit. Now my reception is always top notch. These omnidirectional antennas are available for purchase. I think they cost somewhere around $30.
I would definately recommend going with the XM PCR as oppose to using a stand alone unit.