The Gamecube (to me) was the one that really gave me a great time all those years back. It had some very enjoyable games and the Gamecube was overall a great console.
Nothing beats the feel of Gameboy games that I had a kid, I'd take that thing everywhere... and to this day I'm still discovering so many games I love on it.
So I'll choose GBA, as it has that backwards capability and all them great GBA games too. NDS would be close, as it introduced me to Wifi gaming really, but GB/GBA just holds more nostalgia.