• The DS has a much sharper and brighter screen than that of the GBA SP.
  • The GBA Micro has an even brighter and sharper screen than that of the DS. The only trade-off is that the screen is rather, well, micro.
  • All GBA SPs manufactured since late last year (around September or so) have all the brightness and sharpness of the GBA Micro along with the original screen dimensions. (They're the ones that say "Now with a brighter backlit screen!" on the box.)
So, provided you got one of the backlit ones, you could argue that the SP has a slight visual edge over the DS, if nothing else.