First 3 pics are Forza 2
Last 3 are GTHD
Demo should be pretty close to actual game, since game comes out this month.
Also remember GT was pretty much the game that started racing games. It was the first to use real car exhuast and engine sounds and to closely replicated every detail of the car handling(Remeber the Licence tests??).
Gran Turismo is also a realistic in handling and has great graphics. Kazunori Yamauchi, creator of GT games is a HUGE car buff he is on the Motor Trend 2007 Top 50 Power list:
http://www.motortrend.com/features/c..._yamauchi.html
It is lacking a online feature though, but GTHD was a free download, the full game GT5 is going to have it.