My fave is the one called "Power Macintosh G4"

Depends on what you want to do, but I recommend MDD models. If you are doing any live video work, or encoding - the processor and bus speed helps. If you plan on using X instead of 9 then G4 minis and aluminum powerbooks are the fastest G4 computers you will find. Any G4 can be useful though, unless you are using H264 or other such resource intensive formats. MPEG and other formats in standard definition should be ok.