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

I don't think I will ever part with my Emotive Audio Epifania preamp and Vita amps. I have owned them for over 15 years now (serial #2). Over the years some changes have been made. The original caps have been replaced with VH Audio copper teflon caps (preamp and amps). The preamp's original volume control was replaced with an autoformer volume control, and the plate voltage on the amps was increased to properly run 6550 tubes (originally used 6L6 tubes).
I've changed speakers a few times and am currently using Bache Audio Tribeca's. 

My first decent speakers age 19, were AR2x. I was ransacked years later, took me a lot of years to get over the loss of those speakers.

When I bought my first pair of high end speakers after graduating college. Year 1991 at the Listening Room in Scarsdale, NY. I listened to four different speakers all under $1,000 I think at the time -  Snell, Thiel, Mirage and Def Tech BP10. I remember the Def Techs cause i still have them in my basement storage room havent been used in a decade.  I was blown away by that bipolar signature sound at the time and that's when Def Tech's tower speakers were higher quality. 

A Carver TFM-35 I bought NOS sealed in the original box from eBay in 2009. I still have it.

When hooked up to the Don Sachs preamp gives very little away to his Kootenay. I was surprised that it had very similar upper end resolution. It lost out in lower midrange resolution and bass.
Both things that could be resolved with some careful modification.

Also my Technics 1200G. First upper end component I ever bought. Total end game piece that I will probably never give up.