Which "winning" are we talking about, though? For instance, Nintendo could show a new Metroid and people on the forums and in the audience would go bananas but it would barely move the 'system-seller' needle. Meanwhile, Microsoft could score CoD exclusive DLC and it would have more real-world impact. Forum-goers are often quick to throw out the "won E3" tag without really considering the actual consequences of what was shown.
Anyway, I'm going to pick Microsoft, same as I did last year. E3 is really big for them, I think, considering how the US market is so pivotal to their success. I don't know if anything from Gears will be ready, however, as they really haven't been working on it for very long. I do expect more third-party "exclusives", though, and maybe some true surprises from their new first party studios. Halo 5 will have a massive presence.
We're going to have to go through this again this year at E3, I know, but Sony's strategy has been to raise the value of other venues around the world, which makes sense considering the PS4's global success. They'll have another strong showing, simply because they have so many studios and partnerships, but they won't show their full hand.
Nintendo has Zelda but, with SSB and MK8 released, the only other bomb they can probably drop is another big Mario title, which would surprise me. Hard to imagine them winning with anyone but their own fans. A Wii U Pokemon title might do the trick.
