Stupid thread.
But it depends.
If you want realism go with Forza 2
If you want a more casual experience GT5P.
GT5P has better graphics, but Forza 2 has better realistic racing. The tuning options in Forza 2 are a notch above GT5P. And online is far superior.
I dont see how anyone can comment on either GT5 or Forza 3, as niether is out.