Why is "Yet to come" an option?
The best year so far is yet to come? That doesn't make sense. =)

Anyway, it's 2017. That's the year that Switch got two of the most powerful game releases in Nintendo history with Mario Kart 8 and Breath of the Wild. Yeah Mario Kart 8 came out on Wii U earlier, but that was more like a paid beta, the Switch release was the real deal.

And then there were games like Xenoblade chronicles 2, Odyssey, Stardew Valley, Golf Story, and more. 2019 was also a strong year, but most of the best games on Switch are still from its first year on the market, although that almost certainly changes by the end of 2020. It's not that 2018 and 2019 sucked, they were great, but 2017 was one of the best years of software releases for any video game console, ever. It might even be the best, only year 1 of the Wii really compares, maybe SNES's 1995 or PSX's 1998.

But anyway, Why do I say 2017 without a doubt? In 10 years I can see myself playing Switch games released in 2017. I can't say the same about 2018 or 2019 games.

2019 slightly edges out 2017 for me. Both years were phenomenal. 2018 was good too.

I'm hoping that year 4 will top it all. I am starting to get very impatient for a Direct lol.

I'm currently replaying breath of the wild and I'm actually enjoying it more this time than the first. I said to myself "The Switch may be my favorite console of all time..."

2017. DOOM, Breath of the Wild, Xenoblade 2, Mario + Rabbids, Splatoon 2, Mario Kart 8... impossible to beat so many megatons.

The best year is already behinde it.
2017 had Zelda BoTW + Mario Odyssey + Mario Kart 8 delux + Xenoblade Chronicles 2.

No following year(s) is going to beat that for the Switch.
Those are the biggest heavy hitters Nintendo has, and Switch got them early.

Switch 2020 is like Animal Crossing + Xenoblade 1 +  Tokyo Mirage Sessons FE.... not a big year.
I dont think any year left in the switch will beat 2017.

If you think thats all the Switch is getting in 2020... think again. We still don't know half the story.

Even if Metroid Prime 4 + BoTW 2 also launched in 2020, it still wouldnt beat 2017 lineup.
Also I doubt Nintendo does that, they want to save some to spread out for 2021-2022 as well.

I have more games for my Switch than other console. I have the greatest range of games for any of my consoles (except for first person shooters as I've burned out on them).
2019 was an incredible year for me with games like Ring Fit Adventure, Daemon X Machina & A.O.T 2: The Final Battle but it was also the year played alot of older games like Disgaea 4, Iconoclasts, Toki Tori 1 + 2, Pixel Junk Monsters 2. 2018 was similar to 2019 in this respect and I think this is simply how 2020 will be for me as well. There are so many great games that I've missed that new releases take a step back. I still have yet to play the Dragon Quest 11 demo!
So I think the best is yet to come!

I never said it will beat 2017. But that doesn't mean it won't be a big year. Holiday season will have a big title. BotW 2, Odyssey 2, Mario Kart 9... we don't know what it is, but Nintendo is not gonna let the holiday season go without at least one big gun.

That's just holiday though. Late spring, mid summer and early autumn will most likely have a big title too for each. Like always.

I repeat: thinking that all we are getting in 2020 has been announced in 2019 is silly. 

2017 but damn 2019 was so close as well :) Also the best is yet to come, I'm pretty sure!