I haven't played smash but out of the others I would say Tropical Freeze. I got so many hours out of this game with all the collectibles and 200%ing it in hard mode.

3dworld is also pretty cool but I wouldn't go for captain toad if you're on a limited budget.

i voted SM3DW... but i just realize you need something to play lots and more so maybe until you will be very rich get SSB4.

it will let you play longer.

I would recommend Smash Bros for multiplayer.
For single player Tropical Freeze: it has more depht than 3D world, more content and more replay value.
Also it's challenging, 3D World is mostly too easy.

Donkey Konga Tropical Freeze! It's the best platformer in the Wii U at the moment. The fur looks like something taken out from Pixar, really you can't go wrong with that one.

It's a hard pick, but I'd go with Smash. You can get plenty of your fill with that game. 3D World and TP will have their end eventually, but Smash gets you the most out of your buck. Though all those games are good. Depends on what you want mostly.

this :)

actually all four games are awesome though

Tropical Freeze is a masterpiece. The soundtrack is astounding, the level design of this game is fantastic, and gameplay wise, it's certaintly the best plataformer available on Wii U.

Super Mario 3D World is also a great pick if you are into local co-op, but if you prefer a competitive multiplayer, then Smash is better.

If you like the hobbit and play local multiplayer, Lego the Hobbit.

I bought Captain Toad before I bought 3D World and I regret nothing. Its a game that stands out on its own and its a must buy if you like puzzle games. Otherwise I would buy 3D World followed by DKCTF.

Can't you get both 3D World and Smash? Both are equally awesome! :/