This game would be better for the Wii.
With the DS, you are able to look around using the touchscreen, in about the same as with the joystick of the N64. But with the Wii, you are able to actually hold the camera and aim it yourself.
Wii discs are also able to store more memory than DS cartridges, so the Wii would definatly be able to store the animations, locations and that stuff for all 419 Pokémon (more at that time, because D/P would also be released). The sceneries could also be much more beautifull and expanded. The memory probably wouldn't be the biggest problem, but I think it could be an issue.
The most ideal case would be if a Pokémon Snap came out for both. Both versions would also be able to connect with eachother.