What's the best and/or favorite piece of equipment you've owned? And do you still own it?

My favorite piece(s)  are  (and I still own them) the Martin Logan Ethos lousdpeakers and Soudsmith Paua cartridge.  As far as speakers go, electrostats are my favorite and will replace them with another set of electrostats.  I'm currently eyeing MUR Audio SP1's.  These two pieces make my rig sound great.  
Ohm Walsh speaker owner since 1982. 
Two pair currently.  
It is not my best component, but it’s my favorite component, largely out of nostalgia: My Thorens TD166 MKII turntable. I still own it and use it. I bought it (with my parents’ help) in 1977 or 1978, at Audio Consultants in Evanston, Illinois, while I was still in High School. After 15-20 years in storage, in 2018 I brought it back into the Audio Consultants shop, had it serviced and overhauled, and a new cartridge (an Ortofon 2M Bronze Verso) installed, and put it into service in my system. It was great to see the owner Simon, who sold me the turntable so many years ago, in the shop. While getting the turntable sorted, I also bought several new components from Audio Consultants to get a great 2-channel system up and running. Simon has since retired, and Audio Consultants is now closed, to my sadness and dismay (but happiness for Simon). This may not be a top of the line turntable, but it still sounds great. And, I was loyal to that shop for more than 40 years, having bought many things there over the years.
The Maplenoll Ariadne Signature TT i still own modded with extra arm and 100lb platter and custom motor. Regretfully it makes my large digital music collection sound uninspiring and has therefore decimated my choices  about 80%.
As much as I love listening to audio, when it comes to physical possessions I'm 'way more emotionally attached to my musical instruments and to my record collection. That being said, I guess I got to say that my favorite component is my PrimaLuna Integrated.  Not only does it give me lovely, immersive sound, when something gets noisy it's fun to turn it upside down, take off the bottom and squirt Deoxit on the offending knob.  The 'Luna is so wonderfully straightforward and un-tweaky.  Then again, I've suddenly developed an unmistakable yen to audition a Grandinote Shinai.