1. Nintendo DS - opened up Nintendo to so many different people, got solid 3rd party support, innovative touch controls. 7 years longevity.
2. Gameboy Advanced - apart from having a strong library of its own, it also gave us ports of great classics
3. Nintendo 3DS** - its slowly but surely building a nice library. time may move it up the ranks.
4. Gameboy - doesnt have a huge library but does have a few good classics.
5. Gameboy Color - only 3 years longevity. games could be played on the original gameboy. has less than 5 strong titles