It's going to be a close contest between the three 3's: Killzone, Gears and Uncharted.
Personally I think it'll be Uncharted 3. From the demo I played of Killzone 3 the 3D effect was very impressive but didn't show much beyond that. Gears 3 I believe is still using the Unreal engine and unless they've made some pretty significant changes I don't think they'll be able to push it much further then it's already been pushed.
The demo I saw of Rage at the dev talk I went to wasn't particularly impressive. It looked advanced but the art-style was very reminiscent of Fallout 3 and it didn't top other games already out at the time.
Would be nice to have a look at this when ME3 and Skyrim gameplay are shown. I expect the character models in ME3 will be very impressive like ME2. Not sure on Skyrim, but the scenery in Oblivion was quite impressive for the time so who knows?
