Youkai Watch(hopefully localised), Tomodachi Life 2, Mario Maker, Bravely Third or something from Atlus.

Pokemon and Monster Hunter at launch would grab Japan by the balls and squeeze til they turn purple. 

They should probably focus on Japan foremost, it's about the only place where the handheld market is still healthy.

The new gen of Pokemon launching with the handheld would make it a massive success right out of the gate (and not just in Japan). That's honestly the best case scenario for launch software that would make it an instant success. They wouldn't even have to try with the rest of the launch lineup, though if they did it could really be a huge start.

If the next handheld had only one game ever, and that game was Pokemon, I'd still get it.

Pokemon and Yokai launch would clean up. With Monster Hunter a few months later for momentum.

I think the following: ( and ALL global at the same time and all games localized.)

Yokai Watch
Monster Hunter OR Dragon Quest
a Super Mario Platformer OR Mario Kart 9
New IP
bunch of 3rd party support.
Rayman OR Sonic game.
Metroid/Kid Icarus/Starfox
Twilight Princess HD remake.

And lastly, an RPG that is not MH/DQ/Poke/YW. Maybe Bravely Third.

If they released Pokémon at launch, the console would sell out for months maybe even a year, they wouldn't even have to release much else at launch because the console would just keep selling. When something continues to sell out after launch people start talking about it and wanting it themselves.

Super Mario Galaxy 3 (or whatever the next 3D Mario is)
Animal Crossing Next
Luigi's Mansion 3

Should all be diverted to the next handheld launch window, with Mario Kart 9 planned for post-launch.

I don't think people realize that is going to be maybe the most important launch in Nintendo's history ... if they do poorly, they are screwed because any more losses on the handheld business side weakens them more and they can't afford to have any more slippage with handhelds. Their future as a dedicated hardware maker starts to look awfully cloudy. They must have a great start AND post launch period with the next handheld. 

Also I don't think Pokemon would be there at launch, Nintendo prefers to wait and build up userbase before releasing Pokemon. Capcom probably feels the same way about Monster Hunter 5 ... they'll probably want at least 2-3 million next-gen Nintendo handhelds install base in Japan.

If it's another poor launch, honestly Iwata should be fired too. Three .... *three* bad launches in a row? Get the fuck out, seriously, you can't be a leader of a company and lead a company into such bad situations when you had it in your power to plan better.

The bad 3DS launch did harsh damage to Nintendo and led into several years of losses, the Wii U has never really recovered from its crappy launch. A third poor or even so-so launch is unforgivable.

For once they should be over-prepared for a launch. If it means you have so many games that one or two of them has to be held off on releasing for a month or two to space out all your games, that's a good problem to have.

If you ask me, Iwata's already done enough to deserve to be fired. Wii/DS to Wii U/3DS has been a fucking catastrophe. Time for new management.

OKAY This is a hypothetical best Launch nothing else. Stay on topic kindly :)