Fallout 3 with "Best of Show," but will that translate into sales when the game actually releases? Well, chances are, sales of the game will probably have very little to do with the title receiving the E3 award; however, according to analyst Ben Schachter of UBS, the "Best of Show" does typically go on to see an average of 2.42 million units in sales within the US.
Schachter notes that every software winner over nine years has gone on to see over a million units sold (except for 2000's Jet Grind Radio). He also points out that each of the winners was either a first-party game or a console exclusive*.
*Don't get nitpicky, we're way ahead of those nerdsploding and furiously typing that MGS came to the GameCube six years later.