Asriel on 24 August 2016
This is a tough one. Eventually I went with DS, it has such a huge and varied library, and the DS Lite model in particular was excellent. It looked great, was fairly comfortable to hold, had a superb screen (easily the best screen Nintendo had done at the time), and had access to the GBA's excellent library to boot, which not only included fantastic original games but also had ports of some of the greatest SNES (and therefore greatest ever) games.
3DS would come second for me, because it has access to that enormous DS library, a good number of first class titles built for the system, and some great variety through Virtual Console and eShop.
