GT4, no doubt. I am about to purchase the sexy $150 racing wheel for my PS2 just for this game. Too bad it isnt online.
I am not into all these little street racing games. The racing is far too easy and unrealistic (although juiced has caught my attention). Also I dont care about that bodykit crap and stickers, the real power comes from whats under the hood, not what the car looks like. I play GT3 without no aids at all so yea, I am kind of a hardcore racing game fan. =P
I really hope that in GT4 the A.I. is revamped. In GT3 all they did was follow a set path, real boring. But man... it is a huge dissapointment that GT4 wasnt online... I was hoping to test my skills against others around the world. Also a cockpit view would be nice... I would love to have that witht he right analog stick having you look around inside the car. That is my main gripe with most racing games... no cockpit view, just a view that strangely puts you in between the front two tires.