I agree with the comments on the XL. I have one and I love it. It comes with Flipnote Studio (my kids like it) and Brain Age games. I love playing Virus Buster (a Dr Mario clone) in Brain Age Math.
The large screens are really nice. Can't say it enough about them. I also have a bunch of DSiWare games such as Shantae's Risk Revenge, Dark Void Zero, Box life and a bunch of others.
I will get the 3DS one day when it has come down in price and there's an XL version available. Right now, I have a huge backlog on the DS/PSP/Wii/PS3/N64/PS2 that I can't fathom getting another handheld.