This is a heck of a statement because I still play my SNES regularly. But now that we are in the extreme twilight of the DS series of hardware, I think I can say without a doubt that the DS/3DS system has been the best video game device I've ever owned. That little thing has so many great games, many installed directly to the 250GB microSD. So many great moments in so many great games; plus access to the combined DS and 3DS libraries which are sleek and portable.
And now that prices are coming down on games and systems, I may grab a spare so I can keep it in-box just in case I require a new system someday. This thing still gets a lot of use. The games are cheaper now as well and you can even find them at yard sales.
My SNES will always be the "nostalgia" console, but I really can't sell the DS short. That handheld is the best system I've ever owned.