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

I’ve owned a lot of different components from many companies in my life. So obviously they don’t count.   Speaker-wise, I’m a Maggie Man through-and-through, but I’ve upgraded up the Maggie line a few times now, so I can’t count them either.
I do have two old friends that I will never sell. A pair of McIntosh C-20 preamps. They’re both about 60 years old. I’ve owned them for almost 50 years. They both have been restored and upgraded twice. The last time by Don Sachs. I’ve had them tested and the specs now exceed the original specs by a nice margin.
My C-20s are in a quadraphonic system. They Each sit just before the front and rear channel amps and are restricted to a line-level input coming into the Aux inputs, and then stright out to the amps.
Basically, I use the C-20s for l-r balancing and volume control of each amp and to get that sweet tube sound they put out. This was in place long before the term “tube buffer” came into vogue.
I still think they are the coolest looking preamps in the world IMHO and as I said, after almost 50 years together - they’re like two old friends.
Tim

Dali Helicon 400, Sony TS 999ES SACD player. 

My Berveridge (Roger Modjeski, RIP) RM-1/RM-2 Preamp, since 1981.  Still amazing after all these years.

After many years  in audio and going through so much equipment, I can't say I miss any particular piece of equipment. My present setup is best I've had, I expect future changes will also be upgrades. At this point in my audio evolution I find I'm no longer nostalgic over past components.

If I was to wax nostalgic about any one particular piece, it would probably be recalling the experience of hearing my CJ MV55 tube amp after many years of exclusively running SS amps. Twenty some years later, tube amps only for me. Also, still own the CJ amp, likely will never be used again as Its bettered by all my present tube amps.

My favorite is my 833A single ended triode stereo monoblocks. I could never afford to buy manufactured ones ($350,000 for WAVAC and a "cheap $60,000 made in Poland.) I built my own with all the design features I want and could not count on getting if I could afford one from a manufacturer: polypropylene power supply filter capacitors in a pi network with the chokes on the negative side for grounding safety instead of inferior electrolytic caps, Hammond 1642SE output transformers good for 4kV carrying only 1kV at which by battery polarity reversal tests on the zero bias grid shows the same current change from the modest 20 ma plate current so I know it s respectably linear and which sounds spectacular, The Hammond transformer is good for 300 ma. This is a marriage made in Heaven for Magnepan speakers which are more than loud enough running the tubes so modestly and allow that SET sound without the need for complicated cones, cabinets, and crossover networks that are sensitive enough for less powerful tubes such as the 300B or the 45. I drive the 833A grids through Lundahl transformers with 45s and these with choke loaded mu follower 2C22s directly with no need for capacitors n the signal path. It took me over two years to perfect this system and I desire no other.