It depends on what the author means, the original gameboy advance, or the SP. Personally, the GBC was a better shape to hole then the GBA (not the SP though) and a lot of GBC games are classic, whereas there arent many for GBA.
I'd go Gameboy Advance cuz its backward compatible with all those older gameboy games. I like being able to play all my games on one piece of equipment.
I'm going with the GBA, because it is what I had and it is newer than the GBC. My dad got my brother a GBA from Japan before it came out in America. It was pretty chill.