I am a little bit confused now. Once I consider buy a USB Flash Drive, and some acquaintances strongly recommended to not use it.
My need it is just for Eshop games. I always prefer retail games.
So, it is ok if a USB Flash Drive instead of a HDD ?
I used a USB Flash Drive on my 8GB Wii U Basic from launch right up until Mario Kart 8 came out. I bought MK 8 digitally and it installed onto my USB Flash Drive. It was a nightmare. The game would crash almost every couple of hours and MKTV was unusable. The problem was simple, the USB Flash drive simply could not keep up with the game, it was too slow.
Now I use a 160GB portable Hard Drive with a Y-cable and Mario Kart 8 plays perfectly with no crashes at all.
Also, Mario Kart 8 loading times from pressing to start the game on the Wii U menu to the game loading to the title screen:
My existing USB Flash Drive: 35 seconds
Portable Hard Drive using Y-Cable: 25 seconds