I play NFS shift for a while and just got the GT5.
GT5 has really more fancy graphics, which I already knew as I saw some videos, but I'm really disappointed about the driving experience. I found it very unrealistic, I can't feel the car at all. Everything seems almost always a lot artificial.
Driving is ARTIFICIALLY hard in some points, like driving a rear traction car and losing the line. Even a 63 HP car spins like it had 500 HP (and even if you loose the gas). Seems like the game entered in a "spin anyway" condition (blah!). And, in the other hand, things that should cause problems simply don't: when the car leaves the ground, it lands ALWAYS smooth and harmless just as it didn't happen. If it weren't for the "bump" sound, you wouldn't know about it. I found the physics very poor in GT5 prologue, hope it improves a lot when the final version comes.
Until now, I played both only on controller, but will acquire a wheel soon. By this time, NFS seems way better to me.
ANY car can spin if you don't apply the right type of driving to correct undesirable behavior.
FWD: Brake in a straight line and accelerate all of the way through a corner. You may have to slow down more, but this allows for easier control.
FR: If you are going the max speed your tires will allow in a corner, DO NOT LET OFF! TTO (trailing throttle oversteer) will spin you like a top if you do. If you try to speed up in a corner when at the max grip for the tires, you WILL understeer. Brake however you want and keep the back end in line through the corner and you'll be fine.
RR: These cars drive exactly like a FWD through a corner. On throttle: Understeer. Off throttle: Oversteer. Try to find a good balance and don't let TTO kill you.
4WD: They are fairly unpredictable. One second they could understeer. The next, they can oversteer. Try and learn the car's behavior.
I played the GT5 Demo, GT5 Prologue and shift.
My Shift is on xbox, but i found great settings for controller.
I tried GT5D and GT5P on the DS3 so it wouldn't be a wheel versus controller thing. I also prefer the 360 controller a tad for racing games.
I found that GT5D/P's cars reacted very predictably. The dynamic handling was outstanding. The physics allow for TTO and FR understeer under acceleration.
Shift's physics (set to pro with all aids off) are just TOO EASY. I can NOT get the car to oversteer when letting off the throttle AT ALL. I also can not get a FR car to understeer when flying through a corner. They just don't have dynamic car behavior down in Shift. While the tires in races seem to be okay, they are a bit too grippy. If i can take a hairpin turn in a Murcielago at 60MPH IRL, then sign me up. Until then, the shift tires have too much grip. Weight transfer is great. i can see the car shifting along its suspension under forward accel, lateral accel, and decel (also known as Accel, Turning, Braking/Decel).
There is just something that doesn't add up in Shift. If eA and the game developer rework the physics a tad in NFS Shift 2, then i believe it will be pretty nice. until then, ill stick to GT5