A big part of it, I think: the Steam Controller is different in ways that are unpleasant if you approach it like a standard controller. For example, it is not designed to be gripped around the handles like an Xbox controller, but to rest in your fingers. If you attempt to grip it like a traditional controller, it is uncomfortable and the trackpads are hard to use.
I have a friend who grew to like his Steam Controller after using the trackpads on his Steam Deck. For him, it was realizing the potential of the hardware combined with Steam Input.
I really enjoy all of Valve’s hardware. Others are mentioning the Steam Deck, which is great, but I also love (and frequently use) the Steam Controller and Valve Index.
I don’t know if I have a clear least favorite, as I never owned the things which interest me the least.
I’ve been really enjoying racing in Automobilista 2 with several friends recently. A bunch of us went from using a controller to having a wheel and often a wheel stand in a short period of time, because we all got so into it.
I think there is a lot going for AMS2 (as it is commonly abbreviated): lots of variety in the cars and tracks, it is easy to set up casual races with friends, it is very dynamic (like in varying track and weather conditions), works well with a controller or a wheel, looks good and performs well, etc.
I wrote a Matrix bot that can be used for my community to schedule gaming events. I just pick a time to play a particular game, and play with whoever shows up.