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

I would say my favorite two pieces are an SST Ambrosia 2000 Second Generation Preamp followed by my Focal Sopra 1 speakers.

justmetoo, your answer is a variant on mine, I believe. Imo, it takes many iterations of a system to attain the high synergy that you speak about. Yes, once that is attained, all the gear seems to be "favorite" pieces. It’s like the opposite of the question that is often posed, "What should I upgrade?" The fear is, "What would I potentially lose in an upgrade?"

I have found over time that it is often detrimental to cling to one or two pieces, because usually, they can be bested by another product, and they can be the limiting factor in the system. One cannot know this by emotion, historical comparisons, or hearsay; they have to be compared with a new product to show the reality. Often, nostalgia blocks that, and so, the rig and experience does not improve by changing that particular piece.

But, then again, it takes a LOT of iterations of systems to gain some certainty. 

Audire Diffet 3 preamp.  Rare, but truly excellent.

Yes/no/maybe.

Thanks for the opportunity to revisit memory lane!

NAD 3140, Nakamichi 480, Sony PS-X60 w/Shure V-15 and Celestion Ditton 15XR w/factory upgraded tweeters/networks on Celestion Chrome OEM stands. My High School system circa 1982 when time stood still :-)

Gone but not forgotten.