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

Probably my Totem Arro loudspeakers. Fantastic imaging, tone/timbre, and bass response especially for the size and price.  High Wife Acceptance Factor, too.  I still own them but am not using them now. They were a bit undersized for the room and for some complex arrangements (or high volumes). Oh, and the Wife Acceptance is no longer a Factor.

B&K 202+ power amp.Still have it but it needs repair.

My Aiwa AD F-770 three head cassette deck. 38 years and still going strong with nothing more than a belt change. Also, my Marantz st6000 tuner. These are the only things remaining from past systems.

IMO, once you achieved a very high level of synergy (including your ears/brain) it's VERY difficult, maybe impossible, to pick one single item in one's setup. 
How tricky is it, to chose between Burmester speakers, Levinson CD, DAC, preamp and PassLabs power amp?!? 🥴 
Am I the only one here with such a difficulty in answering the OP's question? 
M. 🇿🇦 

My favorite piece right now has to be a Lyra Kleos cartridge. I upgraded to a VPI Super Prime Scout but installed my old Ortofon cartridge. When I installed the Kleos, it didnt open the door to high definition sound it Kicked the door in with both feet. Couldn't be happier.