For me it would be the Nintendo DS. My parents didn't have a lot of money but still got me one for my birthday, and by the time the system was discontinued I managed to collect like 100 games. It had so many unique and crazy games. One of the last ones I played was Phantasy Star 0. I used to pay PSO on my friend's GameCube so it was nuts to me there was a version on the DS with free multiplayer.
Some of my other favorite games in no particular order:
- Dragon Quest IX
- Solatorobo
- Elite Beat Agents
- Final Fantasy Crystal Chronicles: Echoes of Time
- Pokémon Diamond
- Castlevania: Dawn of Sorrow
- Avalon Code
- Tetris DS
- Mario Kart DS
- Luminous Arc