Nintendo will win with Nintendo fans.
Microsoft will win with Microsoft fans.
Sony will win with Sony fans, then win again with them in December.

Well, it depends. I mainly play PlayStation, but Nintendo can win it if theirs is better.

I never been huge fan of conferences that announce stuff that won't come out for awhile (sometimes games that don't come out for a decade), So I generally prefer Nintendo style.

With that Microsoft seems to have more to lose this conference if they don't announce stuff immediately for the console, so I hope they have a lot of announcements for near future (not distant future).

My money is on Nintendo for announcements I can feel/taste.
My money is on Sony for having just the best conference/announcement.
My money is on Microsoft for letting me down, based on what I said above.

The strange thing is, I prefer Sony overall for my wallet, but a lot of stuff I love do not get showcased at conference either.

Winners:

Sony
Rock Star
Activision

Losers:

EA
Ubisoft
Nintendo

I predict that most people will pick the company they like best as the winner of E3, usually based on the criteria of, "I like their games more." Conversely, they'll call the other conferences "boring" and "terrible" because they had games they didn't like as much. After that, they'll argue that their opinions are factually correct because they have the only perspective that matters.  Youtube views will be called in as evidence.

Such an exciting time.

Personally, I think this will be Sony's most middle-of-the-road conference in awhile (though I've said that before and been very wrong). Not because we won't see video of some quality games but because there is a vocal group of people who only seem to care about big announcements. We already know most of what Sony is working on so there will certainly be some, "OMG WHERE ARE THE SUPRISES WORST CONFRENCE EVER!!" comments.

However, if the pacing is anything like last year's event, I will enjoy it. Prediction -- WINNER

Nintendo should have a quality event because I think they have a lot of unannounced content in the works. They probably won't throw it all out there, though, as the plan this time seems to be to follow a measured and orderly pace. Prediction -- WINNER

Microsoft is the most interesting. What do they have in the works? Do they have any bombshells? Do they have anything at all besides Scorpio making games look a bit better? This is Microsoft. The have the resources to turn this around--provided they don't spend those resources on dancing elephants and strippers. I think we'll see at least two surprises and then a lot of Phil looking trendy with a gaming tshirt and a blazer. Prediction -- DRAW(ers?)

If Nintendo brings out their big IPs + Third Party support then they can win!

Out of the hardware manufacturers?I think MS is going to be the loser, no matter how you slice it, and Nintendo has a great chance of winning this year.

But overall?EA is going to lose, as always.

Well, what Sony studios remain with unannounced games? Sucker Punch, maybe Japan Studio, maybe a third party contract, what else (that's not some little side project)? 

Who wins if all those games are announced?

The same happened with Nintendo a couple years ago when they announced alot of things at the May direct but little on the actual E3.Itsnnot unpresendented.

Now, I do believe Sony will have new stuff to announce.I mean, its easy for them, since they can call third parties and offer them a space there to announce their big new projects.But as far as first party is concerned?Outside of the already announced titles, I dont expect much.Maximal one or two new ones, and thats it.They already have alot on the pipeline of announced titles, I dont think they are working on that many new games that we havent heard of.