Personally I am looking forward to Sony, Square Enix, and Nintendo.
My Predictions:
Sony has a new Uncharted game coming up, and they will probably show us more information about the game and give it a release date. They will also announce a new God of War and Ratchet and Clank game. The Next Ratchet and Clank game is said to be a reboot of the original game's story. We may also see a few nice surprises along the way. Playstation allstars 2
Sony will also probably talk about some random shit like TV shows or Playstation Now or something along those lines. They do have a Ratchet and Clank and Sly Cooper movie in the works. They are also rumored to be collaborating with Nintendo to be working on a Super Mario movie.
Square Enix WILL NOT feature Final Fantasy 15. However, I am expecting Kingdom Hearts 3, Tomb Raider, Dues Ex, and Hitman flavored News. My completely out of left field prediction is that they will announce The World Ends with You 2. I am also kinda hoping that they talk about the new Dissidia game that is being tested in arcades in Japan. The game has been officially stated that it is built on Playstation 4 technology.
edit: oh ya, Bravely Second is a thing.
Nintendo will talk about NX, they will also show us more Star Fox U. Legend of Zelda U has been officially stated to not be making an appearance at e3 this year. I am also expecting DLC news on Super Smash Bros, Mario Kart 8, and Splatoon. I am expecting to see some new maps, characters, stages, costumes, and more. I am expecting to see something big for Smash as well in the form of updates. My prediction for smash is an announcement for a major character who has never made a playable appearance in the smash series. This character will also come with an update bringing along their own home stage on both games. Nintendo has also never dropped information on tournament mode yet. As for character predictions, my gut wants to say Ryu from street fighter due to that Data mine leak. However, I want to say out of left field we will see someone else, like the Chorus Men from Rhythm Heaven. I am also expecting to see some surprises for other game announcements, including updates on the new Rhythm Heaven, Fire Emblem, and SMTxFE games. I am also expecting to see a SMTxFE trailer that will show us the game's official Title. I would also hope Nintendo brings Pokken awareness to the west and announce the obviously going to happen Wii U version of the game.
Lastly for Nintendo, We have not heard from Retro Studios (Metroid Prime and Donkey Kong Country Returns) and Next Level Games (Super Mario Strikers, Punch Out!! Wii, and Luigi's Mansion: Dark Moon) in a long while. I am expecting something big coming from them.
Edit: oh ya, Nintendo said that Amiibo and Quality of Life will not be discussed at this e3.