In terms of odds:

Nintendo 60%
Microsoft 25%
Sony 15%

Basically I think Nintendo has the most available to show and is the most motivated to show it. Microsoft has less available but desperately needs a win. And Sony must be feeling pretty chuffed right now, and I think that they might be sitting on announcements for when they need a win.

Plus, a lot of Sony and Microsoft's big hitters we know to be delayed; unveiling loads of new stuff when you've just told us to wait on the old isn't the greatest of ideas.

Given recent news 2015 seems the clear winner.

I think it will be a very even E3 with respective fan bases appeased in most regards. I'd be very surprised on games alone to see any of the three really shake things up (now watch something happen!).

Sony, when they announce 10 m wonderbooks sold. What bigger surprise could there be? Wonderbook ps4?

Define "win"

Nintendo. They already have Smash and Zelda....and they really need tp push the Wii U so they will show loads more awesome stuff. 3DS always has great games revealed anyway.

Also......X is so hyed! the new Fire Emblem could too.

Sega

Sony.
Uncharted 4, GT7, The Last Guardian, Demons Souls 2, possibly Agent.
Its gonna be mad.

Nintendo could if they show the next list:

Zelda HD
Hyrule Warriors hype trailer
Metroid Prime 4
Metroid Prime Trilogy HD
New action adventure a la Banjo IP made by Retro
X
Bayonetta 2
New 3D Mario a la SM64
Animal Crossing U

Nintendo already wins this calendar year with "luigikart" and "falconPunch:arena"

e3 will be tough cuz everyone is just going to be showing off a considerable number of games. Winning e3 though, will be about changing perceptions. I believe all three have the power to do so, and I think the chances of doing so favor mostly nintendo, then sony, then ms.

In my mind the winner is the company that shows the most impressive upcoming exclusive titles. (bonus points if they are a surprise announcement)

Nintendo and Sony have the advantage of massive 1st party studios. It will be interesting to see what 3rd party exclusives Microsoft can secure to compete. The 2-1 software sales advantage for PS4 of recent multi-platform titles makes is all the more difficult (and expensive) for MS to keep titles away from PS4 in the future. Expect more indie exclusives, exclusive DLC, or timed exclusives for XBO.