These type of threads are pointless on this site because nintendo could just take a shit on the stage and people here would claim greatest e3 event ever.
In any event I would say nobody, they all had pretty major flaws.
EA
It was pretty bad, but this was a major problem
https://www.polygon.com/e3/2017/6/11/15778112/ea-e3-2017-youtube-influencers
Bethesda
I guess it would have been slightly better if evil within 2 wasnt leaked early, also the vr stuff that less than 1% of steam users even have vr headsets, new wolfenstein looked pretty decent though
Microsoft
They revealed new hardware but how will they attract people back is another issue, almost every single game was also coming to pc or timed exclusive, alot of them were indie games and there was no big game announcement
Ubisoft
I really havnt cared about AC games since the ACII trilogy, the rabbids + mario I just have to ask why?
Sony
They really dropped the ball from last year, while there were a few new games announced and gameplay for spiderman (I'm not sure I would call that showstopper) and such, it was just lackluster
they do an get an A for presentation though
Nintendo
While they brought first party games but alot of the bigger stuff like new pokemon and metroid just said now in development with nothing to show, the mario trailer looked really good though. There was non existent third party support except for rocket league and no 3ds, I guess thats dead now?