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

15 year old Magnepan 20.1s, originally $12,500, bought for $5,500 right here on Audiogon. Magnificent sound.

Mac 2105. Still have it after 44 years.

Conrad Johnson Premier 7A amplifier.
That was an absolutely transformational piece for my system.
Followed by Thiel CS 2.2 speakers.
With the Connie J I probably didn't get the low end grunt which the 2.2's were capable of. But the mids, high end and imaging were positively heavenly.

Very fond of a pair of LXmini's I DIY'd last year - inspiring the sale of Tekton DI w/factory upgrade, and they outshine the ML's, B&W's and GE's (floor-standers still have in the stable). Others just can't compete - they all just sound like speakers to me now, while LXmini's disappear and sound real. However, I have not heard many other speakers that might compare favorably in this arena (Spatial, Project, GR-R, etc.). LXmini's do require subs for full-range. ML e-stats share some likeness, but have such a narrow sweet spot. I'll probably always keep a pair of LXmini's (these, or future builds).

Revox B77 and I still have since 1972. It was serviced every few years and still works flawlessly.