Just one question: Can you play GTA:VC on XBOX? No? So now you know what to get

IMO that`s the best game available at the moment...
It`s up to you...which genre you like most.
If you mainly go racing games (like me) PS2 is much better than XBOX. Cuz you have NFS6 (much better than on XBOX), Burnout 2, Gran Turismo 3 (much better than SGT`02 or PGR).
If you like FPS then XBOX might be your choice: Halo and the upcoming sequel (as well as Unreal Championship) are pretty nice. Although i have to say i played Halo some times and i think it`s absolutely overestimated...
If you like action in general then PS2 has just more (and much better) games: GTA3, GTA:VC...and Splinter Cell is coming for PS2 next year too...
Well...your choice...