For me, the DS and 3DS have blurred together. I have very fond memories of playing Phoenix Wright, Layton, and Picross games but would struggle to tell you which was on what system without looking it up.
TWEWY was another game from this era that I loved.
I think I bounced off of all the other common classics. I hated Mario 3D world and New SMB, I really hated Spirit Tracks, Animal Crossing was not my thing.
I did have fun with Tomodachi Life for about a week, however!
By the end of its run with me, the (3)DS was exclusively a Picross machine. Lordy I love those games