Based on the software output:

2017 > 2022 > 2019 > 2020 > 2018 > 2021

2017 have many big hitters and a dozen of 1/2 million plus sellers. Same for 2019 and 2022. Those 3 are the winners clearly. 2020 and 2018 had the stellar hits Smash and animal crossing I, plus a bunch of smaller sellers. 2021 was the weakest year.

Based on my tastes:

2019 > 2017 > 2021 > 2020 > 2022 > 2018

I get the appeal for 2022, but I was only interested in Triangle Strategy and Splatoon last year. Xenoblade and Switch Sports do nothing for me and third party late ports are uneventful if you have them already in other consoles. 2020 was a bit weak too, I played mostly backlog, Animal Crossing and Pikmin. 2017, 2019 and 2021 were great

2017 was very important for the switch, getting out to a great momentous start. And I was along for the ride. Loved playing and beating zelda, played and beat odyssey, and put in around 1000 hours on splatoon 2. Shit, I loved and beat Mario Rabbids too and played the shit outta arms.  Great year.

2017, namely in the last quarter of the year. But even then, there was stuff earlier as well.
-Super Mario Odyssey
-Zelda: Breath of the Wild
-Stardew Valley
-Skyrim
-Xenoblade Chronicles 2
-Mario Kart 8 Deluxe
-Free Online
And there are other first-party games I didn't mention. 2017 had a lot of ports (as every year for Switch has), but that's not inherently a bad thing.
2019 would be the runner-up, followed by 2022. 2018, 2020, and 2021 are all pretty interchangeable off the top of my head as far as the weakest years go, maybe 2018 at the bottom for introducing paid online and having little I cared about other than Smash.
2023 will probably be right around the middle. I am going to get FE Engage and Zelda: Tears of the Kingdom at some point.

Well. 2017 had Breath of the Wild, Mario Odyssey and Mario Kart 8. Can't really beat that.

2017 was unbeatable from a first party perspective, with Nintendo wisely stacking it to get the system off the ground, but third party support was quite sparse.
I guess it comes down to how much you value non-Nintendo games on the Switch.

Not surprising that most people, including myself, picked 2017 as the best year for Switch! A big first year lineup is key to a system's success. Hopefully Nintendo has big things planned for year 1 of their next system. A new Mario Kart and 3D Mario at launch with Animal Crossing within one year would be big!

2017 was the year everything changed for Nintendo. A great set of games released. It was also the moment Nintendo emerged from the ashes of (the very wonderful) WiiU and reintroduced themselves to millions of new and old Nintendo fans.

I have loved every year of the Switch’s life and there’s never been a drought for me, but there is no denying the crazy joy I felt in that first year, particularly with Breath of the Wild and Mario Odyssey.

Hard to top BOTW and Odyssey in the same year

2019 is up there as well I'd say, with the likes of Astral Chain, Luigi's Mansion 3, Witcher 3, Hellblade, Ori and the Blind Forest, Yooka Laylee and the Impossible Lair, Mario Maker 2, Yoshi's Crafted World, Trine 4, etc.

That was the year when third party support really kicked into gear to supplement Nintendo's own output.

This is why a strong year 1 would be very important for the Switch successor ... get a strong year 1 and the rest of the gen is like walking downhill instead of climbing uphill with a poor 1st 6-12 months.

Switch was on cruise control because the first 8 months is particular had 4 huge sellers and system defining games (Zelda: BOTW, Mario Kart 8, Splatoon 2, Super Mario Odyssey). 

Do the hard work early and you see the benefits of it for years to come.