Home Console: Wii most definitely. Galaxy 1/2, Pikmin 1/2 New Play Control, Chibi-Robo New Play Control, DKCR, MK Wii, SSBB, SSX Blur... Virtual Console... BC with the Gamecube (if it didn't have this then GC would be my number one).. The Wii had practically everything I want console-wise.
Handheld: This one is difficult for me between the DS and the 3DS... Resultantly, I think I'll go with the 3DS thanks to it's backwards compatibility. Having access to FE: Fates, Mario 3D Land, SSB4, Pokemon ORAS/X/Y/Super Mystery Dungeon, Pushmo, Luigi's Mansion, etc. In addition to my favourite DS games like both Pokemon Mystery Dungeon 1 and 2, The Urbz: Sims in the City, Trauma Center, Phoenix Wright, Kirby Super Star, Mario Party DS, etc, on the same console, cement the 3DS as my favourite.
If I could only buy one?? I'd probably go with the 3DS simply for the fact that I play my handhelds more.