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

My Pioneer PD S95 Stable Platter Transport. I've had it for probably 15 years and have had no problems with it, although have had it serviced just to make sure all is well 2 years ago. It was beautifully designed and built, and has really been a pleasure to use.   

My pair of BEL 1001 power amps. As close to electronic perfection as I think possible. Whatever you put upstream you can hear exactly what it sounds like. Whatever you place downstream you know exactly what they sound like. As to the amps themselves? Neutral, transparent, nuanced, effortless, refined. I’ve owned BELs since the early 1990’s. I’ve never looked back, never thought there was better out there. 

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.