@Nemix77 Did you even read the OP? Cause this has nothing to do with USB sticks...
@MetoMeto I used a WD Scorpio Black (WD5000BPKT-75PK4T0) in the past but got "USB disconnect" errors. Not sure if they where cause of the brand or cause the drive was old (with many S.M.A.R.T. warnings). Now I'm using a WD Blue Mobile (could give the exact model number later if needed) and am just happy with it. Yes, seek times are higher with the new HDD and I think I'm seeing this in some rare situations but I never measured it, so it could just be my imagination.
BTW; The SATA to USB adapter I'm using didn't want to run with the WD black (had to improvise to get it connected) combined with the Wii U (worked just fine on PCs) but the blue + the adapter works just great on the Wii U.
How exactly should load times be better? The SSD cache is a writing cache mostly (only hot-reading paths are cached but I don't expect the Wii U to have hot loading paths) so reading/loading is limitted to the HDD part of your hybrid drive.
What are you suggesting here? Hitachi, Toshiba and Seagate drives are the worst (failing fast, unrecverable, ...) - and that's not limited to Wii U usage. I'm speaking of 15 years experience in stress-testing drives here...
...is a waste of money as the Wii U is USB 2.0.
Seagate needs a Y-Cable, too. Only because it manages to spin-up doesn't mean it will be stable.
You do know that the sleep feature needs to be cooperated between the operating system and the drive? So you turned the autosleep off on your PC while the Wii U will still use it... And the Wii U is able to turn off autosleep on all drives that support S.M.A.R.T. (which I assume are all drives that exist on this planet). Stop using tools from the drive manufacturer and learn the techniques behind it. Pretty sure there are S.M.A.R.T. tool available which are able to turn off autosleep for your Hitachi drive on Windows, too..