Just gonna list my top 3
Splatoon 2 145hrs
Mk8 deluxe 95hrs
Re revelations 2 80hrs

Top 3: (It includes me and and my brothers)

Splatoon 2 - 335 Hours
BOTW - 235 Hours
Arms - 90 Hours

I've only had my Switch for a couple of months, and I've already done Breath of the Wild on Wii U, but here's the list:

1) Breath of the Wild - 45 hours
2) Xenoblade Chronicles 2 - 35 hours (closer to 40 on in-game clock)
3) Super Mario Odyssey - 35 hours (likely to end up over 40)
4) Splatoon 2 - 25 hours
5) Stardew Valley - 15 hours
6) Fire Emblem Warriors - 10 hours
7) Mario Kart 8 DX - 5 hours
8) Sonic Mania - 5 hours
9) Tiny Metal - 4 hours

I have Lovers in a Dangerous Spacetime and Mario & Rabbids Kingdom Battle to start, and with the exception of Sonic Mania and Tiny Metal, I'm still playing every other Switch game I own, so those times will go up.

Mario Odyssey and Zelda are the only Switch games that i've played, even though i do own a couple more games.

Zelda BotW is at 150 hours...

Xenoblade 2 is over 110 hours...and climbing...

Disgaea 5 is around 70 hours...

Dragonball Xenoverse 2 is at 60 hours...and will climb when I return to it eventually...

Mario Oddyssey is over 40 hours...

I have quite a few more games, and finish the main part of all I have played so far, but anything under Mario I shall not consider part of my "most played" status.

BOTW 195 hours... I would like to go to 200 but nothing else left to do but getting 50+ koroko seeds!

Not Rocket League?

Haven't bought it yet. And even if I buy it one day it will certainly not become my most played game on the Switch.

Fire Emblem Warriros - It's so easy to play for ten to fifteen minutes on the go.

I imagine Zelda will compete once I get around to buying it.

BotW.
I expect DS to be the second one after launch on May.