I noticed both consoles had a similar amount of games for the franchise so I decided to compare the sales between similar games.
Note: Only retail sales considered, 3DS might surpass the DS ones if we had numbers on digital sales
Pokemon Diamond-Pearl (DS): 18.25M
Pokémon XY (3DS): 16.14M
PREVIOUS REGION REMAKES
Pokemon Heartgold-Soulsilver (DS): 11.78M
Pokemon Omega Ruby-Alpha Sapphire (3DS): 12.65M
SECOND REGION IN THE CONSOLE
Pokemon Black-White (DS): 15.18M
Pokemon Sun-Moon (3DS): 14.79M
SECOND REGION REVISITED
Pokemon Black 2-White 2 (DS): 2.00M (at second week)
Pokemon Ultrasun-Ultramoon (3DS): 2.98M (as of second week)
SO, WHICH DO YOU THINK WAS THE MOST SUCCESFUL CONSOLE FOR THE FRANCHISE?