The Fire Emblem and Bravely Default series on 3ds are both as good as any series on other platforms. Wii and Wii U are difficult cases but the DS line has in general been an incredibly good console platform. I actually think it was the best of the last generation. Maybe the switch can carry that on but I'm not sure.
The 3DS has some excellent third party exclusive games, mainly RPGs. I really can't think of anything comparable on the Wii or Wii U that I feel I'm missing out on, except for the first party titles.
A lot of people consider Bayonetta 2 to be a console-seller (though personally, I've only tried it for a few minutes and the intro to that game is super confusing). There's also some other great games that, while aren't exclusive, do have unique features on Wii U (e.g. leveraging the gamepad), such as Rayman Legends. As for RPGs, there's Xenoblade Chronicles X.