3DS is an interesting case. I have more fond memories of DS, perhaps because touch gaming and official online mario kart were new at that time. That said, when I compare them individually, 3DS is a giant. So many games still to play.
I put in WORK for Animal Crossing Wild World, playing with people across US and Europe, but at the end of the day I return and it's like 15fps, has no holidays, and next to no features for MP besides really simple self-imposed games.
Pokemon SoulSilver is timeless, but the competitive planning aspect has been exceeded by later entries. But, it is still the best singleplayer Pokemon.
3DS is objectively improved and better - not even including the fact that it is itself a DS. The smaller models obviously lend themselves better to the DS "upscalling," but the 3DS has had some solid and still active communities of its own. Monster Hunter 4U, for example is reason enough for this to be top-of-the-line.