Recently, an article was posted on the Nintendo Switch homepage which showed the top 20 most played Nintendo Switch games since launch, with GameXplain posting a video demonstrating the list:

The list goes as follows:
1. The Legend of Zelda: Breath of the Wild (Of Course.)
2. Super Mario Odyssey (It's Mario.)
3. Mario Kart 8 Deluxe (It's Mario, again.)
4. Splatoon 2 
5. Minecraft: Nintendo Switch Edition
6. Stardw Valley
7. Mario + Rabbids: Kingdom Battle
8. ARMS
9. The Elder Scrolls V: Skyrim
10. The Binding of Isaac: Afterbirth+
11. NBA 2K18
12. Dragon Ball Xenoverse 2
13. Fire Emblem Warriors
14. Lego City Undercover
15. Sonic Mania
16. Pokken Tournament DX
17. 1-2 Switch (Ohhh, I sense the salt for this one. XD)
18. FIFA 18
19. Disgaea 5 Complete
20. Rocket League

Pretty impressive and diverse list, I have to say. (Though, it makes me sad to see Xenoblade Chronicles 2 not make it.)

But this got me curious, what are the games that YOU guys have played the most on Nintendo Switch?
I'll share mine, with the game and the # of hours played straight from my profile:

1. The Legend of Zelda: Breath of the Wild - 100 hours or more
2. Xenoblade Chronicles 2 - 95 hours or more
3. Super Mario Odyssey - 55 hours or more
4. NBA 2K18 - 55 hours or more
5. Mario Kart 8 Deluxe - 50 hours or more
6. Sonic Mania - 25 hours or more
7. Splatoon 2 - 20 hours or more
8. Mario + Rabbids: Kingdom Battle - 15 hours or more
9. Fire Emblem Warriors - 10 hours or more
10. Shantae: Half-Genie Hero - 5 hours or more
11. Batman: The Telltale Series - 5 hours or more
12. Sonic Forces - 3 hours or more
13. ARMS - 1 hour or more
14. 1-2 Switch - 1 hour or more

The others, I've only played for a little while or are not displayed, since the profile will only showcase the playtime of the last 20 games you've played.

So far, I've played Stardew Valley the most. Zelda will soon overtake that, and Mario Odyssey will eventually overtake both of them.

I was also surprised that Xenoblade didn't make the list either, but perhaps is due to it releasing in Dec. Here's my list:
1- Splatoon 2- 215 hours.
2- Xenoblade 2- 45 hours.
3- Arms- 15 hours.
4- Doom- 10 hours.
5- Mario Odyssey- 5 hours.
6- Thumper- 5 hours.
6- Oxenfree- 4 hours.
8- Mario Kart- 3 hours.
9- The Bridge- 1 hour.

I only have one game so

Splatoon 2

I've only played 3 games so far and as is:
Breath of the Wild at about 70 hours
Odyssey at about 40 hours
SteamWorld Dig 2 at about 10 hours

Update:

1. The Legend of Zelda: Breath of the Wild - 50-55 hours on switch ( i have more than 150 hours on wii u, so..)
2. The Elder Scrolls V: Skyrim - more than 35 hours
3. Splatoon 2 - something around 28 hours
4. Stardew Valley - more than 25 hours
5. Super Mario Odyssey - more than 15 hours
6. Xenoblade Chronicles 2 - around 10 hours (now around 20 hours)
7. Golf Story - something around 6, 7 hours.

i bought nba playgrounds enhanced edition today too, lets see if that game its good to waste some time.

Did you just buy the system?

Zelda: 80 + hours
Xenoblade: 75 + hours
Has Been Heroes: 60 + hours

After that there's a significant gap, I think Mario Odyssey and Splatoon 2 are next at a distant 4th/5th with like 20+ hours

Of course mine is Breath Of The Wild, with something like 115 hours iirc, but Skyrim is at 100 and will overtake it in the next couple of weeks I expect. The other game that I've put a huge amount of time into (over a hundred hours I think, though it’s now been pushed off the page) is Has Been Heroes: I really liked that game but no one else seemed to rate it at all.

Off the top of my head...

Breath of the Wild - 115 hours
Mario Odyssey - 30 hours
Splatoon 2 - 25 hours
Mario Kart 8 - 15 hours
Shovel Knight - 15 hours