mine is Pokémon ultra moon because i like how easy it is to get a shiny in the ultra warp ride. I also really like lunala, and dawn wings necrozma even more.
My favorite games on DS/3DS? Well, the obvious candidate is Meteos, but if I must note others then off the top of my head... DS: Meteos, Custom Robo Arena, The Legendary Starfy/Densetsu no Stafy 5 3DS: Mario Party: Star Rush (an actually good modern Mario Party), and I can't name any others off the top of my head...Although there's a chance LBX would be one if I had gotten around to playing it sometime.
I heard a lot of people think that star rush was a bad mario party game ( but not as bad as MP 9 and 10)
Star Rush is a lot better, aside from a few things (mainly what happens when two people try to grab an ally or balloon at the same time. I enjoy that it tries something new that feels pretty fluid for what it is, and as a one-off idea, I think it's pretty good. (Maybe it could tone down on the Toads a little though XD) IMO all of the Mario Parties are good except 9, 10, and Island Tour. (Advance is a good single player game!)
I have a bunch of them, but some of my favorites are Pokémon (obviously) and the Legend of Zelda remasters for Ocarina of Time and Majora's Mask. Also Link Between Worlds, that one's great too.
Fire Emblem Awakening, Advance Wars DS, or Resident Evil Mercenaries 3D. Mercs is short and I played the other 2 to death, but at that time each was prolly my favorite at the time of playing.