Uncharted 2, for a number of reasons.
Left 4 Dead 2 is releasing a year after the first.
Left 4 Dead 2 is releasing close to the 2 biggest FPS of the year, ODST and MW2.
Left 4 Dead only sold well in 1 region, its unlikely the 2nd will suddenly get a surge from Others.
Uncharted 2 is releasing in a bleak period (as far as i know) for PS3 games.
Uncharted 2 is releasing quite close to the Slim.
Uncharted had good sales in both NA and Others.
Uncharted 2 has won more awards from E3 than any other game. (Maybe not Scribblenauts... not sure)
Sony have finally started advertising.