To the people saying the 3DS version, I have to bring up Smash Run. What part of Smash 4, between either 3DS or Wii U, do people mention as a feature they want to see brought back? It sure as hell isn't Smash Tour. That's the only thing that really stood out on the Wii U version that people talk about as a definitive new feature to that version, aside from maybe 8 player matches, but those are in Ultimate. Smash Wii U is 100% obsolete now. Especially once 3.0 comes out and we get the stage builder and home run contest modes, there will be nothing people are missing from Smash Wii U. Sure people want a Break the Targets game, but they don't want that Angry Birds nonsense we got with Target Blast. They want Melee's Target Test. Even 3DS had something more like what we wanted with the Break the Targets Challenge Doors in Smash Run. Smash Wii U is now an entirely forgettable entry in the series, while 3DS has Smash Run.
Now sure, if they bring Smash Run to Ultimate, Smash 3DS will be a lot more obsolete too, but one thing it'll always have over Wii U? It's not on Wii U. I mean do you really want to drag out your Wii U to play an old Smash game? There are things about that game's meta that I like, but I can always just do it on 3DS, which is easier to take in and out of storage, in fact mine isn't in storage yet, I still regularly play my 3DS and will probably play Smash on it again at some point. It's also portable and can connect with other players locally, which Wii U can't do, and while Ultimate can, I'd much rather not because I'd rather play with the 3DS' controls than the constantly breaking Joy-Cons on my Switch. Damn control sticks can't handle action games without breaking and starting to have that drifting problem. Until Nintendo fixes the Joy-Con stick drift issue, 3DS is the better portable Smash. Indeed, while I use my Switch in portable mode, I don't take it out of the house much, as it doesn't fit in my pocket. So in that sense, even if Nintendo does fix the Joy-Cons, 3DS will always be the more portable Smash to me. As such it will never be irrelevant to me.