Does the Steam Deck count? It became pretty much the only device I'm gaming on since it arrived here.
If not, definitely the PSP, that thing was and still is a beast with some nice cfw on it.
The N-Gage was also pretty awesome. It did many things that people love about smartphones way before anyone even thought about the first iPhone.
Official member of VGC's Nintendo family, approved by the one and only RolStoppable. I feel honored.