I would say pound for pound that the Nintendo Wii U is not only the best Nintendo console, it is the best console period, PS3 comes close but in the end the gap is in the favour of Wii U, in my opinion of course.
Please allow me to list some titles that are playable on your Wii U right now if you wanted. Punch-Out!!!, Mega Man 2, Super Mario Bros 3, Ufouria, Super Metriod, Super Mario World, Earthbound, Street Fighter 2, The Legend of Zelda: A Link to the Past, Super Mario 64, Paper Mario, The Legend of Zelda: Ocarina of Time, Sin and Punishment, Advance Wars, Fire Emblem, Golden Sun and Castlevania Aria of Sorrow.
Not only do you have access to all of these titles, but every Wii U comes with a Wii included meaning you have access to great games like; Xenoblade Chronicles, Pandora's Tower, Sin and Punishment Star Successor, Okami, Resident Evil 4, The Last Story, Tatsunoko vs Capcom, Mario Galaxy 2, Kirby's Epic Yarn, Sonic Colors, Metroid Prime Trilogy and Trauma Center.
With the Wii comes the Wii shop channel, meaning provided you have the controllers you can have access to; Phoenix Wright: Ace Attorney, World of Goo, Chrono Trigger, Final Fantasy VI, Final Fantasy IV: The After Years, Sonic The Hedgehog 2, Ecco The Dolphin, Lords of Thunder and Cave Story.
Mix in all the Wii U disc based software and eshop download titles and I would say that the volume and quality of games available makes it a landslide victory over any Nintendo console. 2nd place I would put the Wii due to it's amazing library and true GameCube backwards compatibility, if you really love GameCube games I could see someone placing Wii over Wii U and it's up to your opinion really, but for me it's gotta be Wii U.