Toss-up between BCP Wave 6 and TTYD, but I think my partiality for the former might just edge out the latter because Funky Kong is an apotheotic being.
Mario vs. Donkey Kong would be my pick. While it's not a new DK-style Mario platformer, this is better than nothing. I hope that it's successful enough to convince Nintendo that we want more Mario platformers of this style.
The new Peach game is certainly interesting. I would like to see how that turns out.
Luigi Mansion 2 HD might open possibilities for more 3DS to Switch ports. (The only ones that I can think of at the moment are the Zelda remakes and the Mario and Luigi remakes).