I know it's not according to the game, but I believe Bethesda won E3.

Doom looked amazing and with id Tech behind it, it could easily be one of the best FPS to come. Fallout 4 looked really great: a talking protagonist, the robot which can actually speak names you've given your characters, costumizable weapons, houses and power armor, jetpacks, huge Boston area. Dishonered 2, the first game was probably one of the best stealth games in recent memory and if the game looks anything like the trailer, we're in for a treat.

EA had Battlefront, but that's about it. Sony and Microsoft had some interesting new IP's and Sony had some big announcements. But I'm dedacting points for the Shenmue 3 kickstarter and timed exclusivety of FFVII, The Last Guardian looked cool though. Ubisoft announced a new South Park game and some more Ubisoft games (you know, the Ubisoft games). Nintendo... had a fun conference... Star Fox looked nice... that was about it, not enough new big games.

So yeah, I think Ubisoft had the biggest announcements.

1. Sony - TLG, Horizon, FFVII Remake, Shenmue 3 and more Uncharted 4
2. Square Enix - While their presenting was subpar, I really did like the games they showed and Kingdom Hearts 3 looks so fucking good.
3. Microsoft - Really solid conference, probably the best for 2015 games, and backwards compatibility.
4. Bethesda - Fallout 4 was amazing, but the rest I found just ok.
5. Ubisoft - Pretty solid conference, but nothing unexpected.
6. EA - The pacing was awful and while I do like sports games, they just took up too much time. However, Mass Effect, Mirror's Edge and Battlefront were great.
7. Nintendo - Definitely the most disappointing conference. I'm glad we got release dates for games like Xenoblade Chronicles X and Yarn Yoshi, but that couldn't save the digital event.

Naah maybe 3rd place

No way. i liked Bethesda but they blew their load ahead of time and besides nothing can beat the trio of Last guardian/FF7R/Shenmue 3. Nothing! As much as i like Fallout 3, its just on a whole level.