Taking into account only exclusives (which I think its what this thread is intending given the poll) its gotta be Mario Kart 8 Deluxe.
Yes, perhaps its mostly a WiiU game, but its still the best for me. The best in the series and the best Mario spinoff ever, incluiding all Mario Parties, Smash Bros, Yoshis and Luigis Mansions. I cant put into words how much enjoyment I've had with that game. So yeah, its the best. For me, that is. 

Following it:

Breath of the Wild
Astral Chain
Xenoblade Chronicles 2
Link's awakening remake

I suppose Fire Emblem 3 houses would be my 6th, but theres a significant margin between them. I still have plenty of issues with it. 

So hard to choose. BOTW. Odyssey, Smash, FE, Astral Chain.

Breath of the Wild is just on another level so my vote goes to this masterpiece. If I had to choose a Top 5 it would go something like :

1. BotW
2. Hollow Knight
3. Super Mario Odyssey
4. Celeste
5. Smash Utimate

Favourite: Breath of the Wild

Most hours played: Splatoon 2

BOTW is number one for sure, hard to beat the 100 hours of just plain fun exploring every nook and cranny. Fire Emblem Three Houses, Mario Odyssey, Mario Maker 2 are all very close. With as much fun as Fire Emblem is, I can't believe I failed to play previous versions throughout the years. Mario Maker 2 is my ultimate I have a few minutes just going to play a few quick levels, and Mario Odyssey felt like what I wanted on the Gamecube for Mario, not that Sunshine was as bad as others say it was. This is the first generation where I've gotten into some of these indies as well, usually I got bored with them quickly. For indies Golf Story, Blossom Tales, and Celeste are my top 3 and I enjoyed them so much.

Breath of the Wild, probably the game of my life

If I could, I would erase all my memories about BOTW just for the sake of discover the gamme all over again

Also loved Mario Oydssey (favorite platform) and currently addicted to Fire Emblem Three Houses and Splatoon 2

So far the only game I didn't like at all was Pokemon Sword

BotW, no comparison. Working on my third playthrough of it right now. Some of you that are on my friends list may have noticed, too. :p

Honestly, BotW is worth $360 as far as I'm concerned. And this is why I am so particularly excited for BotW2.

I would've gone with BOTW as it's the #3 best game I've ever played, but I was voting based on the Switch games I actually have, and I played/own BOTW on Wii U.

Besides, looking at the poll, it clearly didn't need my vote. :p

I said this as well from day one.  If the Switch had no other game release on it other that BotW I would have felt justified in my purchase of the Switch.  And yeah, BotW 2 is going to be amazing.  Wouldn't bother me one bit if they waited another year or two to release it as well, considering it has some pretty big shoes to fill.  Just please, please don't release it near Metroid Prime 4.

Favourite: Breath of the Wild

Most hours played: Splatoon 2