Don't really know about modded tbh, just know it can't play them officially

Counter argument, the 3ds is easier, portable, and almost as useful. Granted, the Wii U allows more titles, like BoTW and Mario kart 8, but out of experience, I can say that the modded 3DS is very good. I have no experience with a modded Wii U, but I'm relatively sure it's not better than the 3ds, aside from storage capacity

I think wii, but make sure it's an alder model. It has a slightly higher chance to break, but allows you to also play gamecube games. If you prefer more backwards compatibility, get a Wii, but if you want more power, you should do Wii u