buy a 64GB, it will be plenty enough for at least a few years if you don't buy big games like Zelda on the eshop.
Most eshop only titles are 1 or 3 GB. And VC titles are really small.
I have a 32GB WiiU, and I have only a 32GB usb stick, all my digital games are installed on it besides Tekken Tag 2 (17GB and it's a crappy game so ) I have at least 20 digital games, plus all the DLC installed for Smash, Splatoon, Mario Kart (I don't own Smash DLC, but wether you own them or not you have to install them), the 2GB of GHlive etc.
Trust me 64GB is plenty enough. Also, buy a decent brand, not a noname from china.







