owch.. that's a tough one.. ask yourself which genre you like more- street racing or simulation? realism or speed?
personally i'd go for need for speed.. (despite the last few in the series being disappointing)
ahh.. read some reviews...

Hm... I think that Shift will be better for you because GT5P is like an expensive demo... there are less cars and less tracks, no career mode, etc. So if you want to get value for your money, I definitely say go for Shift. Then, GT5 is out next spring and you can get the full thing then

Um, probably Dirt 2 and the new GT is coming out soon I think.

Well I don't have a PS3 or an X-Box 360, I only got the Wii. Well for new-age consoles anyway. Cuz I also got a Gamecube, Nintendo 64, Playstation 1 and Playstation 2. I don't think my Playstation 1 really works anymore though sadly. Hmmm, those sounds like good racing games for the Playstation 3. Well I guess I would go for the one that you feel most comfortable playing with and has controls that aren't too hard or frustrating, so I guess Need for Speed's also got my vote. Might I ask why you can't just get both of them though? Well anyway, I should try and get a PS3 just to see how awesome those games Motor Storm Pacific Rift and Burnout Paradise are.

Forza 3 is awesome Sorry, I just had to rub your face in it. Is GT5 ever going come out? What's the prologue that the full game isn't?

@nightmare_fan17: I would but ya know, $$$ dont grow on trees now does it? XD
@dan_scfc: GT5Prolouge is like a glorified demo of GT5. It has about 40 cars and 5 or 6 tracks.

I'd go with Need For Speed Shift seeing how Gran Turismo 5 Prologue is not a full game.

I agree with everyone here who has posted so far:

* Gran Turismo 5 Prologue is nothing more than an expensive demo. Gran Turismo 5 Prologue received very mixed reviews that were disappointing; it has a score of only 80 on metacritic.

* Need for Speed Shift is considered an excellent game that many people enjoy. If you are only considering Gran Turismo 5 Prologue and Need for Speed Shift, there is no doubt that you should get Need for Speed Shift.

* Dirt 2 may in fact be the best racing game on the PS3. I bought the Xbox 360 version because there are so many more people to play with online and the Xbox 360 has that awesome force-feedback steering wheel that is just like you are sitting in an arcade cabinet. If you can, I highly recommend trying out Dirt 2 -- the graphics are awesome and it is fun to play.

* Waiting for Gran Turismo 5 is not a good idea. The game has already been delayed multiple times, so who knows if it will actually come out in the first half of 2010. Gran Turismo 5 Prologue disappointed a lot of people, and it's important to keep in mind that Gran Turismo is a game series that has been in a state of "decline" for quite a while now.

* Burnout Paradise is awesome! I agree with you on this, so I know we have the same taste in games!

* Forza Motorsport 3 is by far the best racing game I have ever played. The graphics, gameplay, number of tracks, real-life damage to cars, are all absolutely amazing! Trust me, just download the demo on Xbox Live and you will see for yourself.