Thinkpad X280, i7 quad w/ 16G memory and 500G SSD. It was on clearance since the model is a couple years old, but holy crap this thing is fast. And so much lighter than the last system I owned with a fast quad core (4-5 KG). My last computer lasted me almost a decade, so with the rate technological progress has slowed (barring M1), this system should last me 15 years or so.
Other than that it would have to be my Unicomp model M repro, or the plants I've filled my home office with. All together it has made the experience of being a technical human so much better.