What is your firmware version?
If you're below 10.5:
Dont buy sky3ds and follow a
tutorial to play 3ds for free.
If you're above 10.5:
If you only care about playing 3ds games easier, just buy a sky3ds and drag an drop. If you want to make your device future proof, just use sky3ds to downgrade, install custom firmware and play games straight from the home menu.
Either way, if you want to play Ds games you're going to need the r4i.