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

My favorite: Thiel CS2.2 amber wood speakers. My first true audiophile purchase in the 90's. I enjoyed listening to them for decades.  Amps, pre-amps, and sources came and went, but the Thiel CS2.2 speakers were a constant. Just traded them in for about $500 less than I paid ~30 years ago. $500 / 30 years < penny per day listening cost.

I upgraded to Thiel CS7.2 speakers, so no regrets.

Fisher 500C Vintage Tube Receiver. Two on the shelf.

Anytime I need to change, sell, fix tuner, preamp or amp, this baby comes out of retirement, keeps the system truly enjoyable until ____ is back in town.

Pair of Vintage Fisher 80Z mono tube amps, pair and a spare on the shelf. Not going anywhere.

my efficient speakers, I never needed anything more than 30 wpc, could probably go lower, just never tried.

ATC SCM100ASLT loudspeakers. Listening to them right now.

The oldest unit I have is Sony CD707ESD
purchased 1990 still use with Schiit Bifrost 2 DAC.
The second oldest is Mondial Designs
Aragon 8008BB amplifier purchased in 1996 still in use with some tweaks love it.

For me it would have to be my Kef 104.2s and my Ayre CX-7e red book CD player.  After almost 20 years, I'm gonna send it back to Ayre for a 'tune up and lube", that's how much I enjoy the sound form this piece.