I would say Brawl because it was somewhat of a classic, its pretty awesome, and of course, it has WiFi. I also think the Conduit had a big release though, and if they had made Super Mario Bros
Wii with Wifi, it too would have been a huge hit. Bad decision Nintendo!
Im not a fan of the
DS, so I don't pay attention to it much. There have been several big releases for it too though.