Go an put hands on to the systems.
I have played the 3DS and it gives me a headache.
The DSi isn't that old, so there aren't any OLD games, they still sell the systems it's not old.
The games for the DSi can be played on the 3DS but not the other way around because the 3ds games are in 3D .
The 3D effect on the 3DS can not be seen at all angles it has to be held in a certain angle and a certain distance from you it to work. I personally don't think the extra features the 3DS has are worth the extra $$.
Now if the camera isn't the selling point look into the DSlite, it plays all the DS games as well as having a second slot for playing the older nintendo handheld games.