Your single favorite component

Of all the pieces of your system you now own or have owned in the past, is there any one piece you could say is your absolute favorite piece of equipment? 

I don't know if I have an answer to my own question - I enjoy various pieces of equipment for different reasons. A turntable I've owned for 18 years, a 40 year old tuner, an amp I built myself, all in some way are pretty special to me. And so on! 
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My Maggie 3.6 speakers. The sound of your system is mostly determined by the speakers and I love my Maggies
My Deja Vu Audio amp, pushpull EL-34's it's totally bulletproof and sounds fantastic. Plus it was made by a great company that's local to me and still going strong.
My bottlehead preamp followed closely by my herron phono stage. 
My ears.

Never owned them but Dunlavy SC IV-A speakers are the best I've heard. Second:  BEL 1001 Mk V mono-block amps.
I greatly appreciate all of my current components. The OP specifically says to name one. Coincident Frankenstein MK II SET amplifier,  getting it was a transformative experience for me. 
Garrard 301 turntable with Ortofon 309 D tonearm and EMT JSD S75 cartridge. The EMT cartridge is simply spectacularly good.
Just like the OP, I don't believe I can name a single favorite component. I have had a few favorites over the last few decades.

I would say my favorite CURRENT component is my VAC 160i SE integrated amplifier.
My Thiel CS 2 2 speakers!......followed by an Audio Research LS25 preamp and my 'ol throwback; NAD 7400 PE receiver.  Great forum.  Regards........

i will say that the one thing I've had longest and has withstood the test of time is my Zerostat.

if i was absolutely forced to choose, my speakers are an amazement. 
i will say that the one thing I've had longest and has withstood the test of time is my Zerostat.

if i was absolutely forced to choose, my speakers are an amazement. Revel Studio 2's. 
I love my Rowland components, but my Monitor Audio PL500 speakers are my single favorite component.
My McIntosh tube preamp
Dunlavy speakers (have almost all of them) still remain the standard by which I judge all other contenders.
My KRELL 450mcx Monoblocks
Love big iron
and they double as space heaters in winter
My Tron Syren Pre.
To hear it is to fall in love
It's a tie between the original Quad ESL and the London Reference pick-up. Then the Townshend Rock turntable.
Vpi Prime and our ears
My Aerial 10t speakers.
Clearaudio Champion Level 2
My PS Audio DirectStream DAC.
I like them all together but Ohm speakers are the MVPs. 

My Harbeth 40.1 speakers top my list. 
Most of our favorite component is speakers. From there we can derive easily what mostly influences sound. Did anyone mention any wire or tweak or rack?

yes, one tweak - Zerostat, and it's a great tweak
love my zerostat. back when i used to do darkroom work, I used it their too 
though I prefer the Mapleshade version
I did like the zerostat.  Had one many years ago.  Are the newer ones the same as originals?
Pass Labs's the best amp I've ever owned. 
My opera audio  consonance reference 6.6 kt-66 tube amp , I have had more expensive amps but this one I've kept .Chris
It's a tossup between my Audio Note Kits Kit 1 SET amp  and my Spatial Hologram M4  open baffle speakers. Together, they are just sublime. :-) 

Hands down, Esoteric K-03 SACD/DAC.  Had one and sold it, replaced with an Ayre.  After a few weeks sold the Ayre and bought another K-03.  A phenomenal player in my system.

Herron Audio VTSP-3A line stage.

An Atma-Sphere UV-1 tube pre. But not just any UV-1...this was the original prototype. It is hand wired point to point and signed by Ralph Karsten and marked as serial #1. Besides the great sound, the uniqueness really appeals to me.  Truly a one-of-a-kind.    Not to mention it's a tube rollers dream.  Lots of vintage 6sn7s at reasonable prices. 
WOW, that's a tough question to answer, but I recently replaced my Paradigm S8V3 speakers with Wilson Watt Puppys, and just love the difference that they have contributed to my sysem
Ok, this will seem strange. I love my entire system which I researched and purchased mostly here on the 'gon. My favorite piece however is my new equipment rack. I purchased the rough sawn hard Maple from an Amish sawmill and then a friend of mine who does high end woodwork allowed me to help him build it in his shop. He showed me how to perform tasks using various tools and throughout the Winter we completed the four shelf 48" wide, 20" deep rack. Each piece was rough sanded by machine and then I hand sanded them prior to finish. You can't help but love a component that you helped to create. It looks awesome! 
New to the A-Gon' but appreciate reading everyones blog posts.  Ive been enjoying my little David Berning tube MicroZOTL HPA!  Is fantastic
It is a 1950's Valvo Cca 6922 Pinched Waist I acquired a couple of years ago.  It is in a (now antique) Audio Research LS2B MKII remote preamp.  Has long ago been a tube roller (roll em in and roll em out) to get to Grey Plate Cca 6922 Siemens & Halske  as the dream of the crop for this pre....   so far removed from that OE Chinese drek....  but this again moved performance to a whole other level.  Just add a finned tube cooler modded with a drain wire to ground to kill some additional RF and there you go.
and on second thought I have lots of favorite components. I really like my modded Acoustat 1100 speakers and the two Sumo Andromeda IIA's that drive them bi-wired on custom cable.  Not to miss the crowd is a Radio X modified Sansui tuner and Magnum Dynalab Signal Sleuth and half mast whip.  Sony SACD which is killa on red book rounds out the list... 
PrimaLuna Dialogue HP Integrated Amp.  No contest.  This thing changed everything.
I've had many but my current "love" is a newly acquired Esoteric SA-50 CD/SACD player.
Quad PA One headphone/pre amp which I re tubbed with Shuguang black bottle treasure cv-181s

The best 12 hundred English pounds I ever spent

Now all I need to do is save up for those Audeze LCD 2s
I would have to say that my BEL 1001 MK5 (made in 2007) is the top component in my system. 
I have had many an excellent component and/or speakers over the years but I would have to say the Platinum Power PP-1 high current balanced power conditioners I use in both the main rig and the HT are indispensable in providing ultra clean/solid balanced power and without clean power, every component that utilizes AC power is handicapped IME.
No.1 would be my DIY speakers which are similar to Western Electric 753 monitors from the 1940s but use an Altec compression driver on the 32A horn.  Details are on my system page.

No.2 would be my Emotive Audio Vita power amps.  I have had them for over 5 years and they are still my favorite amplifiers even for high-efficiency speakers that don't need their power.
Nakamichi 682ZX cassette deck.
My gone but not forgotten Spendor SP100 speakers.
My Magic Eraser. 
#1. my TT, specifically...
- the audiomods arm, performs and looks great
- the Soundsmith upgraded (Denon) 103 cartridge - a superb upgrade

#2. my Simaudio Moon phono stage

#3. my Gershman Acoustics Sonogram speakers

#4. my cables.

Lastly my Naim 5i integrated amp and Schiit Bifrost  DAC

All together, superb synergy!!!

Happy listening :-)

AR turntable; Advent speakers, or Tom Holman's apt pre-amp

... or maybe one of my Advent cassette decks or one of the Naks I had...