I got my son a DSi XL for Christmas when he was almost 8. He had wanted one for years. We have never yet connected it to the internet, though.
I liked the XL for the bigger screen. Honestly, I did not know much about them, so I asked my 6th grade students and they steered me in the right direction! LOL They did tell me that the 3D one was not that great, which was what I had also read in reviews. Not sure if they even make the 3D one since we got his a couple years ago.
One good thing we found is our library rents out games. That saves on costs and the disappointment of saving allowance money only to find that the game is not that great!