Hmm.....I'm probably going to go with 2014 because of it probably having the best Direct theme and presentation with a lot of good games. I liked the puppets in 2015 but not enough with it , and this years Bowser joke was perfect, but it was just really that.

Maybe if Bowser kept trying to host parts of it....

2016, easily.

That was the year they showed off Breath of the Wild, and really that was all they needed to show.  I had waited for 25 years for this game to be released.  I really couldn't believe they had made it at first.  But I just kept watching, every damn minute from the Nintendo Tree House, I kept watching this game.  My wife was like, "You're watching too much, you are going to spoil the whole game for yourself."  But I was like, "No, they are only showing off one tiny region.  This game world is going to be huge, and the gameplay looks amazing.  I MUST HAVE THIS GAME!"

The best part is, the more I thought about it, the more I realized that the Wii U era of suck had ended.  This was a new kind of software that they had made for their new system, "the NX".  The games would be as fresh as the Wii, but they would be for traditional gamers instead of the new Wii market.  I knew, even before the Switch was announced, that it was going to be a successful console.  (Of course I didn't know it would be the best selling console of all time until after the official announcement.)

2010.

The Nintendo 3DS was unveiled, and there were some quality first and third party games shown on Wii.

Two moments really stand out for me:

and

(Well, this one wasn't the E3 trailer, It was from January 2017, but I liked it a lot more). 

Incidentally, my two favourite console games of the decade.

But this E3 was the best one of all time IMO:

And here is the Xenoblade Chronicles X treehouse:

Interesting that 2016 and 2018 got votes in both the "Best E3" and "Worst E3" thread.

Quite divisive and controversial shows those two.

I can’t say anything about worst E3 because I don’t really remember any of them other than the stuff that stood out. It’s mainly what they have done with the “treehouse event” that has made it stand out for me. Otherwise it’s a bunch of trailers, and I usually don’t recall which Nintendo Directs played those trailers.

2016 stuck out the most to me with the tremendous amount of Zelda coverage, so I consider it the best. My second favourite is the one with all the Xenoblade Chronicles X coverage, but I don’t know what year that was, or even if it was E3.

2016 is about what you think E3 is for I suppose.  They presented what they wanted to present very well and it was very effective.  It was also almost entirely one game.

2018, it's literally a matter of whether you like Smash.  It had some good announcements like Dameon X Machina (which I know wasn't dynamite at launch but was a very cool surprise at the time) and Super Mario Party being the first good MP in ages.  And the DLC for Xenoblade turning out to be as massive as it was. And some cool third party announcements that unfortunately got leaked.   But there's no getting around Smash being so much of the show.

2019 had the best-paced presentation. Standout reveals: No More Heroes 3 (very funny trailer), Trials of Mana remake (with a beautiful melancholic musical number to start off), Panzer Dragoon remake (my friend had to try and restrain me), BotW 2 outta nowhere (spooky).

2017 had the Cappy trailer (very jolly), the Metroid logo ("OH SHIT! OH SHIT! OH SHIT! OH SHIT!" Vince_McMahon.gif), and the Samus Returns reveal.

2014 had Splatoon (the ink puddle opening gave me chills when I realized it was a new 1st-party IP) and the Zelda Wii U teaser ("2015"). Oh, and this:

As much as I love Splatoon, the E3 2014 direct itself seems rather slowly-paced when I re-watch it. And while Panzer Dragoon was spectacular, Sega announced something was being done with the IP half a year earlier, so it wasn't as big a surprise as it could have been. So, I have to go with the jpeg presentation, 2017 gets my vote.

Honorable mention to 2016, hats off to whoever made all the BotW trailers.

2017.

Nintendo won my heart for ever with this last trailer:

A 3D Sandbox Mario game where you can possess things, and in 60fps, best thing ever

It kind of comes down to how you felt about the game that was spotlighted those years.  2016 was all about Zelda and 2018 was hugely focused on Smash Bros.  On the other hand the two series that have grown the most on Switch are Zelda and Smash Bros.  Clearly those two games were worth spotlighting.  But if you weren't particularly a fan of that one game that got the spotlight that year, then the show probably seemed like a dud.