you can use both but its reccomended to use a hardrive

thanks

I personally use a usb stick but you can use any... I was going for 128GB but they were sold out so I went for 64GB

i used 2 8gb drives to use with my wii u lol it cuz i didnt have any spare laptop hdd yet but now i have it with a enclosure

final answer, i say its flash drive since its easy to setup and compact but you might snap it if it in a certain position or knocked it (if your wii u is in standup position)

please do not use USB flash storage, as it's not intended for constant read/writes. you should use a HDD, though it may be necessary to use an external power source.