Ok so Heres some screens from each game. Post more screens, debate, whatever. But my vote clearly goes to PGR 4. It's astonishing that game. 

Shift

GT5

PGR 4

GT5, no competition.

The GT games always turn out to be among the best looking games of each generation

haha!
Awesome thread, but difficult to tell when some shots are not in-game (i.e. from replays) and not in motion.
From these stills, my vote goes to PGR, with a nod to Shift.
GT5 seems to be too shiny and artificial edges/bad AA are all over the place in those pics.

Well PGR4 looks the worse as normal :| Its the oldest. IMO when it comes down to realism GT5 still leads, while NFS:S... well it looks good, especially the interiors, but tbh the outdoors look way to blured, and as allways Im expecting the game to look inferior then thye screens that EA release ;)

I must say though, PGR4 looks amazing

Sorry but next to PGR 4 GT 5, especially in cokpit view is not the best. It's to obvious. You should see some of the PGR 4 screenshots taken by the community. Seriously scary.

@Selnor

You'da voted for PGR4 just because it's 360 exclusive anyway=P

As for my opinion, I'd rather not make one based off screen shots, so I'll wait til the games come out=P

GT5 isnt out yet so its hard to say. PD has said that GT5 will have better graphics then GT5:P so they say anyway. So i cant pass judgement on it yet.

As for out of shift and PGR4 both seem to suffer from some serious blur going by those pictures but im liking shift a little bit more over PGR4 as the interior isnt blurry nor is the cars in front. Only blur being used it to give a feel of speed. While PGR4 in those screens are focused on the track with a very blurred interior.

BTW those GT5:P in car screens are wierd.. the side mirror and rear view mirror are heavy with pixelation which in the game isnt there. Its actually clear and you can see whats coming behind you. So im guessing a very early build of GT5:P or GT HD in those screens.

My vote goes to Shift. See in the last screen how you can tell that the camera is pushed to the left side by the g forces?
Of course, that's not GT5, is GT5 Prologue (one and a half years old now) and we know those are actual in game screens.
Somehow I doubt that the other two will look as they do in those screens.
But if they do, hat's off to them :).

 In these pictures you're right, but I have no doubt at all that when GT5 releases, it'll be one of the best looking games to date and most likely pass the other two racers in the OP. Polyphony Digital are Sony's best graphical team, better than Naughty Dog with Uncharted (which is amazing)