Easily Uncharted 2, considering Sony will most likely bundle this is some form and we'll likely see retail with Uncharted 2 deals as its a first party game.
It should also be noted that the Pre-order charts for L4D2 and U2 is almost neck and neck, considering that the First L4D had more than 80% of its sale in NA (whereas U2 sold more in Others than in NA), this is a good indication that U2 should perform above L4D2 worldwide.