Nintendo should win because they have the biggest hardware (3DS) and software (Zelda) announcements in store.
Sony might have a chance at topping them, but only if they announce PSP2 and plenty of big software (Killzone 3, etc.) alongside a killer LBP2 demo.
Nintendo easily has the best upcoming news, but Sony might be able to outdo them by having more things to show that are almost as good.
I'm not expecting much from Microsoft, given that they've already shown off sequels in three of their four big franchises (Halo, Gears, Fable), and only recently released a game in their fourth (Forza). Aside from that, they seem to be focused primarily on Natal at the moment. We'll probably see a new IP or something out of them in conjuction with some third party, but other than that it'll be Natal games and a Gears demo.
