Gameboy color...good old days when i use to mostly play pokemon and mario on it. Also my first game console was also NES. I believe my first game on it was a tank game idk the name tho lolDS is most successful in Japan because it has tons of Japanese games and its mostly popular among students both in school and university especially when commuting to and back from school.
In my opinion the most successful hand held ever made was the GameBoy, I didn't own one but used to play on it with my cousin. I owned a PSP though, but its controllers were very tedious to use. My first console was a NES ( nintendo entertainment system) yes that elegantly designed mystery Pandora's box