There's no way to assess who "wins" an E3 at all...and even if there was a "winner" it doesn't make a difference to reality of who "wins" the "war" or whatever.
It's all opinion's. Last year my opinion was:
-Nintendo won: a new (needed) confident frontman in Reggie, a near flawless NDS unveiling (originally it was a product that might only get a couple people clapping, but when it was unveiled everyone clapped), Mr. Iwata came out to speak of Nintendo's future also with much confidence then the mega-surprize game in Zelda...all around Nintendo had the best pre-show ever
-Sony, eh: boring PP from Kaz, non-flashy intro to PSP...they could've done way better, but they decided not to 'cos they knew the Sony zombies would drool over the "sexiness" of PSP regardless of how boring the presentation
-MS, loser: only one "big" announcement which meant hardly anything...woo...EA on XBL, pffft...they obviously lost pazzaz in their pre-show 'cos their competitors were showing off new hardware
But that's opinion. Nintendo haters are gonna say Nintendo's show sucked last year and vice versa...so what's the point?
This year I think:
-Nintendo will try to recreate the magic they had with the previous years pre-show conference, I think they've realized the semi-importance of these conferrences to their lacking image (GDC, where Mr. Iwata typically cryptically said that the industry needed "saving", this year he instead made several awesome announcements regarding NDS & Revolution) and they're not gonna sit back and let the competition get all the spotlight, I think they'll start out quick/strong with announcements for current systems (new PokeMon for GCN, new Zelda trailor, possible GCN pricedrop and/or redesign, new peripherals for it & GBA, NDS no-line network), they'll poke fun at MS for coming out too soon and talk about how they're still supporting the current generation with some big games, then I expect people to be SHOCKED by the Revolution's design/power/features...most people are expecting another toyish, plastic, pastel colored kid machine that's gimmicy & underpowered ...they will be shocked, I expect that everything will be revealed about the system *except* the controller interface, it'll be all wireless, going online, have more features than exected and be more powerful than X-BOX 360...then the surprize game will be Mario 128 (or whatever the Mario will be for Revolution) and that Mr. Miyamoto will come out PLAYING the game (in other words, not just video form, it'll be played in real-time) with the new interface as a mega-tease without giving away too much making all want to know how it works and what it's about...this will generate buzz...people will walk away thinking: wow, it doesn't look like a toy, it's more powerful than X-BOX 360 *and* the new interface looks like fun
-Sony, I think with new management & new focus and an understanding that MS is going for a knockout X-BOX 360 unveiling that they will *lose the bordom* in their presentations...PS3 will be made out to be more powerful and more spectacular than X-BOX 360 and I think Sony (with the BR group) are making crossroads with the BR vs HD-DVD (if you've been paying attention to that recently, the two formats may be merging so as to not stagger a next generation disc format) and the PS3 party *may* be the time to let loose that announcement and then Sony can poke fun at how X-BOX 360 is for the "HD era" without a HD disc format, Sony will also focus on showing that they want to create a bigger/better XBL-like experience for PS3
-MS, having the full unveiling of their next system and the most next generation games announced plus playables will no doubt have a GREAT show...but with them basically going first they have alot to be worried about, plus there will be the shaddow of doubt cast by the cutting short of the current X-BOX and their competitors announcements of their next consoles...the most buzz will be about X-BOX 260 since it's closer to fruition, but every time it's mentioned reporters, developers, gamers will HAVE to say something about PS3 as well...and if Nintendo shocks enough people, Revolution as well