Reddit reviews HORI Battle Pad for Wii U (Link Version) with Turbo - Nintendo Wii U

Breath of the Wild only supports the Gamepad and Wii U pro controller.

You do not want that PDP Samus fight pad. They suck, and will not work in Breath of the Wild. Also, the PDP pads are literally Wii Classic Controllers, requiring a Wii Remote to use. Not necessarily a negative, just something you need to know.
If you REALLY want a Wii Classic Controller shaped like a GC one, get the HORI Battle Pad.
This also will not work with Breath of the Wild.

If you want the amazing Gamecube Controller shape/Feel in your Zelda, you want THIS AMAZINGLY AWESOME PIECE OF TECH (Also available on Amazon and I think Gamestop).
That is a Wii U pro controller shaped like a GC controller, and works with all Wii U games that support the pro controller. The main reason this works where the other models mentioned here don't is that it features clickable analog sticks. The buttons/control sticks sometimes get desynced when entering and leaving the home menu, but a quick hold of a,b,+,- for 3 seconds will fix any and all issues.
Battery life is excellent, and I have no real complaints.
Only weird thing about it is that the 'Start' button is actually the console power button. To pause your game you'll probably just press + or - as usual.

Hori makes a controller that is functionally identical to a a GameCube controller, which plugs into the Wiimote. The Wii sees it as a classic controller. here is the one I use with my Wii. It's compatible with Wii and Wii U.

Splatoon's motion controls are absolutely the thing to use. They let you aim faster and more precisely than what's possible with an analog stick. It's the same sort of advantage over a stick that you get with mouse aim on PC FPSes, but less so.

As for Smash, if you're used to Gamecube controllers but don't currently have one, the Hori Battle Pad is the way to go. It plugs into the Wii Remote (it's essentially a Classic Controller) so you'll need one of those too. If you already have at least one Gamecube controller, get the adapter. This only works with Smash but the Battle Pad works with any game that supports Classic Controllers.

If you have an ethernet jack near your Wii U, get the wired network adapter and say goodbye to unstable or dropped connections in Splatoon!

Definitely, no matter what, get a Pro Controller. I also recommend two Wiimotes and Nunchuks.

oh man, I got stuff for you.

1. You need a Classic Controller. I suggest getting one of these as they work just as well and they're fairly common to get.
   
   
2. Know that with a Wii U you have two options for the Virtual Console which is the eShop AND the Wii Shop. The Wii Shop has WAY more Options for Virtual Console then the Wii U, but if you want all the games that were on the NES Classic then you need to utilize BOTH Wii and Wii U shops.
   
   
3. Wii Virtual Console games CAN NOT BE PLAYED WITH THE GAMEPAD. This is the reason why you need a Classic Controller. The Wiimote + Classic Controller will allow you to play these games.
   
   
4. On Wii U virtual console games if you want Co-Op, The Gamepad is always going to be on. If you want one person playing with a classic controller and one with the Wii U Gamepad, you're going to need to either press ZR on the Gamepad or just touch the Screen when the Virtual Console game is on and you will need to touch the Bar with the squares to change the order of the Gamepad so the game will know which controllers have priority. Otherwise Both the Gamepad and the Classic Controller will register as player 1.
   
   
5. Here's a little list of NES games I have on my system to give you an idea what's available to own for your Wii U.
   
   :Wii:
   
   

• Super Mario 1, 2, Lost Levels, 3
  
  
• Metroid
  
  
• Zelda 1 & 2
  
  
• Kid Icarus
  
  
• Megaman 1-5
  
  
• Double Dragon 1&2
  
  
• Blaster Master
  
  
• Bubble Bobble
  
  
• Super C
  
  
• Wario's Woods
  
  
• Donkey Kong
  
  
• Gradius
  
  
• Final Fantasy
  
  
• Dig Dug
  
  
• Ghosts'NGoblins
  
  
• The Adventures of Lolo
  
  
• Star Tropics 1 & 2
  
  
• Bokutte UPA
  
  
• Shadow of Ninja
  
  
• Tecmo Bowl
  
  :Wii U:
  
  
• Balloon Fight
  
  
• Punch-Out
  
  
• Castlevania 1-3
  
  
• Earthbound Zero
  
  
• Ninja Gaiden 1-3
  
  
• Kirby's Adventure
  
  
• River City Ransom
  
  
• Megaman 6
  
  And that's just the NES titles I have and that's not even HALF of what you can own.

Ask and you shall receive.... http://www.amazon.com/gp/product/B00ZUNOX9G

a friend of mine gave me this joypad for Wii U: is there any adapter to use it on Switch and GameCube?

Hori Battle PAD Zelda Gamepad https://www.amazon.it/dp/B00ZUNOX9G/ref=cm_sw_r_cp_apa_i_G7s7Bb6TN70VV

https://www.amazon.co.uk/Super-Smash-Bros-Controller-Nintendo/dp/B00ZUNOX9G

They were on Nintendo's Official Store, but randomly disappeared.

Worth mentioning there are more designs, such as a Pikachu one, a Lugi one, Link, Metal Mario, DK, Yoshi, Peach, Wario, and Samus. There might more designs, but that's all I found.
Regarding quality, they are officially licensed by Nintendo, so they should be good.