I was thinking, picking one from those titles.

New Super mario bros.

Castelvania: OofE.

Chrono trigger ds.

They look great to me. Solid buys.

Lunar Knights is one of my favorite ds games.

Those 3 are all ace! :)
It really depends on what kind of games you like, but The World Ends With You, FFIV, Zelda Phantom Hourglass, Tingle's Rosy Rupeeland, Kirby Canvas Curse, the Phoenix Wright games, Animal Crossing, Rune Factory, Mario Kart, Elite Beat Agents and Hotel Dusk are all awesomely sweet games as well! :)

If it was me I'd go with chrono trigger.

The three are great buys.

Just buy all 3. If you have to choose one. I'd say go Chrono Trigger.

Any of the three would be a great purchase. Really depends on what kind of gameplay you prefer.

I absolutely adore the Phoenix Wright franchise and the FF remakes.

I would say Bleach Blade of Fate mostly since it's made by Tresure and anything they make turns into greatness..