Favourite: Steam Deck, hands down. It has totally revolutionised the way I play games. I very often choose to play games on my deck instead of on my far more powerful pc.
Least favourite: Smartphone. The closest I’ve come to having an enjoyable traditional gaming experience on a smartphone was Sky: Children of the Light but even then I was constantly getting frustrated with the touchscreen controls and dealing with my phone getting as hot as the surface of the sun. Its also just not a comfortable shape to hold while you game.