I have a 3DS, but not a WiiU.
you should swap, 3ds has considerably worse library, lets take an example, Mario 3d vs Mario 3d world, xenoblades vs xenoblades X, huge difference in graphics. Pikmin is the most dramatic difference, its really bad on the 3ds, a joke compared to the pikmin 3. Then lets compare Zeldas, ocarina of time is nowhere near wind waker, twilight princess and breath of the wild, not to mention I can also play ocarina of time on the wiiU. Then theres more marios, galaxy 1 and 2 etc.
For half the 3ds generation I only cared for monster hunter 4, but on wiiU monster hunter tri win it for me due to graphics.
Most games on 3ds from top 10 lists are a huge disappointment, pokemons is a terrible rpg where you just go around doing combat all the time and collecting pokemons, theres no story or exploration or puzzles or anything else. Fire emblem sounds great but its so boring, repetitive, nowhere near how fun advance wars was. Metroid samus is only a 2d game, and gets repetitive, I didn't bother finishing it, I much prefer Metroid prime trilogy on wiiU. Bravely default I got 10 hours in, got bored, repetitive 2d stuff, way worse than final fantasy in the 90's Nowhere something like Xenoblades X
Other games like Mario golf, Mario tennis and so on, are made far too easy, just look at the difficulty of pikmin 3 compared to pikmin on 3ds, totally different stuff. Animal crossing was too childish for me, I really tried, I liked the idea of a sims like game, but sims is more adult oriented so Id play sims instead or any of the several great strategy games on ps4.
Smash bros is also nowhere near other fighting games, for example why would Mario and link be in the same universe? Makes no sense to me.
Kirby is good but way way too easy for me.
Xenoblades on the 3ds, despite you needing the newer model of 3ds, it looked terrible compared to the same game on wiiU. And Xenoblade chronicles on wiiU didn't look close to xeboblades X either.
My biggest disappointment on 3ds was kid Icarus, many people were praising that, so I bought it, when I played it I could not for the life of me understand why people were praising it, it was worse than mediocre.
New super Mario bros was also way too easy on 3ds, took the fun out of it.
I really don't understand why Nintendo fans bought a 3ds instead of the wiiU. Its a gaming anomaly. Most 3ds games don't even make me use my brain to play. Just far too easy.