I'd be tempted to say Kirby...just.
Reason being its an overhauled Switch 1 title through and through, so it runs really well, and got a nice resolution uplift. The expansion included in the Switch 2 version is also exclusive; and it's just overall a nice game with some cool stuff.
DK however is fantastic fun, albeit can be a LITTLE one note, but its still VERY fun, and frankly there is so much destruction it would have run like **** on Switch 1 or had to be pared massively back.
Pokemon ZA is actually much better than I was expecting on Switch 2. It runs so much better than Switch 1, and looks considerably better due to the DLSS implementation on top. The real time combat is a blast, but the game feels a bit unfinished, and whilst the map has some depth to it, its still limited to one medium sized city.
If you're agnostic, the real answer might well be, whichever you can get for the best price lol