The Switch only has 32gb of internal memory
Some more Legend of Zelda: Breath of the Wild minutia (Minish-uh?) for you: the game is 13gb on Wii U and 13.4 on Nintendo Switch. They’re both out March 3 and I doubt the .4gb will influence which one you buy.
It is worth remembering, though, that the Nintendo Switch only has 32gb of internal memory, so Zelda alone could take almost half of it. Thankfully, for those going digital, you can expand this amount with any micro SD card. Or clear your Wii U out ahead of time, if you’re hesitant about buying a new Nintendo.