Which one should i buy a 3ds or ds/dsi/dsi xl?

The answerer that said 3ds is correct! The 3ds actually will not harm your eyes at all, even with the 3d on, and the 3d is as easy to turn on and off as it is to push a volume slider up and down- you just push a 3d slider up and down to turn it on and off. Or disable it in the menu. The DS/DSi/DSi XL cannot play 3ds games, but the 3ds can play all the DS games as well as 3ds games!