I think the Game Boy Color was the most innovative. I didn't buy one of the first GBs because I heard that they were coming out with a Color one. Sure the SP's light is nice, it just doesn't revolutionize the gameplay.
No but it did revolutionize accessories and size. The sp had better sound then the gameboy which was more fun. The sp had a built in light playing at night you didn't have to worry about bot aving a acessory light. and finally the sp size was much smaller yet bigger screen revolutionized into the making of small hand held systems.
I would have to say the SP because it changed the look of the entire Game Boy saga. With a built-in backlight, rechargable battery, and portable size, it was a Game Boy like no other.
I explained this already. The graphics on the gba were already magnificent, but the revolution of accesories was a big boost i believe. Having a built in light was truly amazing up to this time. Also the compatibility of it. It was extremely tiny and light wieght. This set the stage for the ds' light and for future game systems to come as well as the psp.
I thought the color was the most innovative simply because it, well... it was the first with color! The Advance enhanced graphics and the SP brought accessorys. But I remember my first GB Color game was LOZ Link's Awakening DX and I liked the one color dungeon and simply seeing it in color.
Advance because it had alot of features you could use with other things like the gamecube, plus you were able to play all the other games on it, SP was just an upgrade