I would say it has a three hit combo as far as killer apps go.

Mario for classic 3D platformers, something we don't see enough of these days.

Zelda for those looking for a massive adventure with countless hours of discovery and exploration.

And Xenoblade 2 for those waiting for a great JRPG to jump into. And boy is this one great!

So seeing how all three if these apps can be considered "killet apps" and they all draw different types of gamers, I would call it a three hit combo and list them as equals.

In the west, Zelda without question. It's one of the small number of Nintendo IP with the power to pull in people who aren't especially interested in most Nintendo games. It has a different vibe.

The Legend of Zelda: Breath of the Wild

The killer app for the Switch?

It's not a game. It's this feature. I'm not even joking.

Honestly, I don't think they have a "killer app" right now so much as a "stuffed library" by the standards of a recent launch. They don't need any one game to sell their console at this point.

Really, I think the closest thing we'll see to a true "killer app" will be the Pokemon game. If it's a decent upgrade over the usual handheld experience and provides something that feels like a console Pokemon experience they could pretty much take the rest of that year off.

There's definitely quite a few of them.BotW, Mario Odyssey, XC2, Spla2n, I'd say there's enough on the Switch to warrant the purchase.

Probably BoTW and MO

Definitely Zelda. It had a > 100% attach rate the month it was released.

Zelda

Arms and splatoon shouldnt be on the same list as BoTW & Odyssey, MK8.
Those 3 have much more "draw" than the others.