For me it would have to be a tie between my switch 3ds and PSP as they are 3 of the best consoles I have ever owned game library wise and wherever I got at least 1 never leaves my side.
My Pokémon 20th anniversary 3ds. I dont normally splurge on special edition stuff, I really like the look of these and I really needed a replacement 3ds (my old one's hinge snapped badly.
My most cherished one I have with me is my N64--many an hour of Mario Kart 64, both Pokémon Stadiums, and the three Mario Parties (and maybe a session of Zelda in there on occasion) was played there
For me, it is a close call between my SNES and my special edition Super Smash Bros. Switch. The SNES is one of the consoles I've been playing most of my life and is just beloved to me. My Switch is the only special edition console that I own, so I treasure it.
I'd have to say my imported Vita or my imported Super Famicom. The Vita has an excellent form factor and a game library that perfectly fits my niche. Playing games on my Super Famicom has been great Japanese practice. It's a solid way to have fun while being exposed to another language.
For me, it's probably my black and blue 2DS I got in 2014 (I think?). This funky square-shaped thing has been with me for 8 years, more or less, and we've been through some wonderful times. Still works perfectly fine today. The worst thing that happened to it was replacing the battery when it started to balloon.