I think most name brand ones like SanDisk are pretty good and work with the Wii U

Can you put a 128gb SD card in the ¨new¨ 3DS models?

yes you can do that

But to answer your question, a 64gb samsung sd card should be good enough for most people (which is what I have in my 3ds).

Yeah bro, use Sandisk after ye Living Computer Brain Storing Homes stop using all yat ram & is costing me ænglisc to oncierran, donde hine forhtian þæt ram weorþ sy upp astigende, *amdi wrixliandz, atiz hwerbaniz razdo iz untw allan* *(e)i- tohi prh2 wohi (su)esio ka yas.*

a 64GB SD card sould work for most people but if you like downloading games you sould get at least a 128

1TB Sandisk SDcard works in the 3DS assuming you format as fat32 with Godmode9

Will the Samsung Switch 2 Micro SD cards work fine?