Of all your gear, what piece impresses you most?

I like all my gear, yet the single piece that blows me away the most is my phono preamp.
Tough choice, since I like all of the components in my current system. Sort of like one of the Commandments from "Animal Farm": "All animals are equal, but some animals are more equal than others". I can fairly easily choose my favorite two components, however: my VPI Classic 3 / 12.7 tonearm combo, and my Vandersteen 3A Signature speakers.
The cost.
We all acknowledge every component is important for overall system success. Staying within theĀ  theme of this thread I'll say my SET amplifiers in a "photo finish" win over my line stage.
My B&W 683 3-way loudspeakers !!
I think as we move forward, it is typically the latest addition that we like most. Perfectly reasonable, in my estimation.

I don't make that many changes over time and my system stays the same for 2 or 3 years before I try to get to the next level. My speakers and preamp are over 10 years old; the SACD player 3 years old; and the power amps a couple of years old.

With that preamble, my amps do impress me greatly, probably more than the other components. I did not think they would improve the sound as much as they did. I was wrong.

Lamm ML2.1 SETs

Purchased a PBN groovemaster, with sme 312s tonearm, and I can't believe the increase in performance it gives me.
Knee-jerk reaction would be my Tannoys, but I've been a fanboy of them for a while now, so it's no surprise I love my current Canterbury SE; I expected to be impressed.

I'd say I've been most surprised & impressed by my preamp, the Rogue Audio Hera II. It's also surprised me twice: first when I got it (used) as an original I (almost 6 years ago), and then a couple years back when I had it upgraded to II status.

I bought the Hera on a leap of faith, and it was awesome; a hugely audible upgrade from the 99 Magnum (which itself is a nice pre). That started a big electronics/analog upgrade run in the rest of the system that's lasted years. At one time I was even set on swapping out to another excellent preamp, but ended up gravitating back to the Hera.
Agreeing with general consensus, my choice components are an equal integral part of the whole. Recently my amplifiers have decided to not work with the team (family) so they were relegated to stand in the corner....
...... which had not rectified their un-cooperation. Stay tuned...
My system all came together when I installed the Atmasphere Novacron monoblocks. But for that to happen the rest of the system had to be wonderful.

(Dealer disclaimer)
My speakers which are a one-of-a-kind 2-way using a 15" paper cone woofer designed in the 1940's, an aluminum horn also designed in the same era, and an Altec compression driver from the 1970's. Any combination of these drivers would probably sound pretty decent, but what ties it all together is the crossover which uses some equalization to tweak the response. In my admittedly biased opinion, this speaker combines some of the best qualities of vintage speakers such as Western Electrics (musical tonal balance with sometimes startling dynamics) with modern audiophile qualities (high frequency extension, detail, imaging). This speaker also has a wonderful coherency---despite the very different drivers it sounds like a single driver. The roughly 98 db sensitivity also allows use of low-powered amps.

If I had to, I could live contentedly with other turntables, other electronics, other cables, etc. but these speakers are a necessity!
I'm most impressed by my Grace F8 cart by a bit over the NSM sub. The Grace presents my vinyl in musical ways that surpasses previous carts, from Grado wood-bodies to ZYX. When I read about the setup and integration issues folks have with their subs, I feel lucky to have a sub and manufacturer support that was so easy to place and have a seamless sound with Fostex driven main speakers.
Bel Canto ref1000m monoblock amps because they are everything I could ask for in an amp in a very small and non-obtrusive package. Modern technical innovation applied to home audio at its best.

Also the latest addition, a Pangea power cord, just because of the build quality and heft plus it looks awesome (as power cords tend to go).
My tube amp, because it appears to be alive. Otherwise my modest (priced...bought stuff cheap or used here and there) system doesn't seem to lack anything it might need for musical enjoyment at this point, so I'll change things only out of boredom, curiosity (would a different TT sound better?...hmm), esthetics (I like striped ebony...I want some speakers with striped ebony veneer), failure (a component, not my personal failure, although deafness or sudden death could have an impact and shall be avoided if possible), or everything (except me) falling down a sinkhole...hate those sinkholes.
It's a toss up between my Artisan Fidelity Garrard 401 with upgraded platter and inverted bearing, and my Jeff Rowland Continuum S2 integrated amplifier.
My 10 year old Von Schweikert VR5 HSE speakers. I simply cannot find any flaws in them no matter how many components or cables I change.They give daily satisfaction.

Well my 2 cents (a bit more than that...) - the 2 most important parts of an audio system is the source (and to be more precise the dac) and the speakers. Hence I will pick the dCS Vivaldi dac and the Vivid g3 speakers.
Maybe my choice is do to my other components or possibly the other way around but I would have to say my
Tron Syren Full Function Pre Amp.
In a word Fantastic !!!!
Vivid Giya G3 speakers... cuz I paid so much...
The gear that impresses me most is not necessarily also the most irreplaceable. There are many very good amps and power cables in the sea.......
The Phonostage (Omnigon) & Fidelity Research FR-66s Arm
The BSG QOL unit.
2nd place is the Synergistic Research HFT's.
I'll follow Charles' lead and claim a photo finish between my Ayon Triton amp and the Duelund CAST caps in my speaker crossover. I believe both are significantly helping provide the clearest and most holographic soundstage of any system I've ever owned.
I consider my system to be well balanced, however I consider my BEL 1001 MK V to be my most valued component. Probably most difficult to replace from either a sonic or cost basis.
It varies.
The Tube Research Labs Dude preamp has been a complete game changer for every system it has been part of in my home over the many years. Rarely does one piece have such a profoundly positive impact on a myriad of different systems.
My honorable mention is the Offramp with matching Dynamo power supply from Empirical Audio. They made my ears smile big!
My ears
Great post. Amen to our ears!
My SET amps, because they took a year of my life to build...and they actually work!

The Midlife Crisis

Ait, oh my blank!! I have to see more pics of your awesome amps. Where can we go to see them? I would love to see your build as they look like absolute DIY or extreme DIY. Nice job and congratulations!
I have to cop out a bit here, and declare a tie between my Avantgarde Duo Omegas and my Lamm ML2s - the synergy between these components is priceless.

Not so far behind: the AMR CD-77.1 CD player, and the Cary SLP-05 linestage.
No ties allowed LOL.

You can follow the entire build here, from conception to completion, including schematics, Spice and PSUD simulations, photos of the parts and sub-assemblies, test results, philosophical debates, etc.:

Building A Midlife Crisis

Very impressive, Congratulations !

Good Listening

What impresses me the most in my system are in this order, Von Schweikert VR-33 speakers, Audible Illusions Modulus 3B tuber preamp and Odyssey Stratos Extreme+++ or something like that. Those are 3 pieces I will never sell. In addition, the Odyssey Kismet Reference Floorstanding Speakers which I have in my office system. For a 2 way floorstanding speaker, the sound is to die for.

I read through most of your thread and am so impressed with your skills. Congratulations on perhaps the finest SET amp to grace any music room. Certainly one of the very finest!
My de Capo's are amazing monitors. But the LSA Statement integrated is also a lifetime piece.

Truthfully, it's the Rotel 1072 cd player that performs far out of its league.
My comfy couch, so that I can sit back and enjoy all of my system and just take it in. . . who knew.

Modwright KWI-200 w/ MW LS-100 PA.
My Berning zh270, 12 + years of ownership and frankly a product that has to date not shown me ANY limitations with the right speaker. It is in demand for good reason, the value/performance/efficiency quotient is unparalled compared to any amplifier I'm aware of for ALL the genres of music I listen to. Limitations that's the key word. While no product is perfect or ideal for all applications, or tastes for that matter, some just get closer to the ideal, this one does for me. It has never stopped amazing me since the day I purchased it and along the way, the tweeks to enhance it's performance.
My turntable cartridge. Such a small device to make a huge difference in sound.
@ AIT, Man!, I have to agree with Grannyring, what an awsome pair of amps!, what brand and model speakers is that you have in the pics, you still have them, they are eye candy as well, how do they sound, what are the specs on those babys?
The headphones...Sennheiser HD800.
A basic rule in audio - change only one component at a time.

Fortunately I had experience with each system component prior to buying the Janszen zA2.1 speakers. So there is no doubt in my mind they have impressed me most.

So soon I hope to experiment with other upgrades, including a new room later this year.

Those are Infinity RSIIb speakers, circa 1985. I've completely redone them with an external passive crossover featuring NorthCreek and Solen Heptalitz inductors and Mundorf and Duelund caps, new midrange diaphragms from Apogee Acoustics, rewired them with Cardas copper litz in teflon. They are excellent sounding, and not an easy load for an amp, but the above SET handles them beautifully.
My Ref3 preamp. Nearly ten years old and it still makes the hair on the back of my neck stand up and gives me chills. It is amazing.
My Rogue Cronus Magnum.
North Star Design-Sapphire. Price/Performance ratio is off the charts!
In my case it's a no brainer: the Wavac HE 833 V2 150 wpc SET mono blocs. Outrageously beautiful in sound and looks.