I would say get Smash while everyone's playing it, but most people probably play the Wii U version anyway. If you have a Wii U, get Smash for it. If you don't, then maybe get Smash 3DS if you know people that play it.
I don't have a Wii U but I have Smash for 3DS, and I wish I could afford the Wii U version because everyone's playing that all the time. Although if you don't know anyone who plays Smash then I'd say Zelda is a better single-player experience.
Majora's Mask 3D is a remake of what I think is best game in the series, but if you've not played Zelda before then I'd recommend getting Ocarina of Time 3D instead. If you like OoT then consider MM.
Numberwang. But also Smash 4.
In response to the comments on Ocarina of Time the game is difficult to come by as a physical copy since Nintendo no longer produces the cartridges after the release of Majora's Mask 3D. Nowadays, they go for $60 used and $90 new on most websites. Luckily I bought a copy of OoT back in December 2011 but I'm hoping to be able to grab a copy of Majora's as well before they stop making them as well.
Harvest Moon: The Tale of Two Towns 3DS, Fire Emblem Awakening, and Happy Home Designer