Is an autoformer (AVC) always superior to pots and resistors ?

Autoformers, transformers, optocouplers, potentiometers, resistors I have all of them. My friend the late Roger Modjeski preferred the old Noble 100k or 50k potentiometers which we have plenty of and sell to folks who want to DIY a simple pot-in-a-box. It takes a lot of pieces to come together to get the best out of any of them. Never tried a buffer in my system, but Nelson Pass seems to find them helpful and they would be just to have that control over the output impedance. Like active preamps they have their warts as well, but with active devices its all about the circuit, that will define the component.

In my digital system I use either a Lightspeed attenuator or AVC I built myself using the top level Slagle Autoformers. In my analog system I use an active preamp because I need the gain for LOMC and analog tape. @atmasphere is right about the rules, the only other thing the transformer will give you is galvanic isolation.

Antique Sound Labs used to make a preamp that used either an AVC or TVC as the attenuator (I can't remember which) with a tube output. Way back there was a well regarded active preamp made by Melos that used optocouplers, this before the Lightspeed I use came on the seen. So the technology has been used before in different applications with various levels of success.

Like many things in this hobby, there does not seem to be a clear-cut performance hierarchy between TVCs, AVCs, volume pots, and discrete resistor switches/arrays. The reviews I have read of TVC and AVC offerings mostly paint them as nothing short of the crème-de-la-crème of preamplification. Reviews of EM/IA, Townshend, Music First, icOn, and Bespoke are all extremely positive. On the other side of the coin, I have read about their susceptibility to ringing, as discussed earlier in this thread, and possible difficulties processing complex, dynamic music. The many positive reviews left me intrigued enough to look at trying an AVC or TVC preamp for myself.

I have the icOn 4PRO balanced preamp here now. It is a Model 4b, which is fully balanced, including 4 Slagle autoformers, and offers both balanced (XLR) and single-ended (RCA) inputs and outputs. Functionally, it seems to be at the top of the pile of TVC/AVC preamps in that it offers fully balanced processing of the signal, remote control of inputs, outputs, balance, mute, and volume, and a very nice segmental display that is the easiest to read of any I have owned. Sonically, most of the reviews I have read are hesitant to call out significant differences between the better known options such as S&B TVCs, Slagle AVCs, or even the Bespoke TVCs. There does seem to be a clear preference (by many but not all) for silver wired TVCs or AVCs, which cost about twice as much.

I initially thought I would probably like the icOn as a passive volume control in front of my SMc Audio unity-gain buffer (using a Hatter discrete resistor passive preamp in that role now), but surprisingly the icOn seems to sound better as a stand-alone preamp connected directly to my amplifiers. Even though it has RCA inputs and outputs, in my system I seem to like the sound best when using the balanced inputs and outputs. One nice feature is that you can select which output (or both) are live, so I use the balanced outputs for my main amps and the RCA outputs for my two subs. Since I have only had the icOn here about a week, my final subjective assessment compared to the Hattor/SMc combination will have to wait, but I can say that the icOn sounds good. However, based on what I have heard so far, I suspect it will be a close call on which I ultimately like better in my system and for the music I listen to.

Like many things in this hobby, there does not seem to be a clear-cut performance hierarchy between TVCs, AVCs, volume pots, and discrete resistor switches/arrays.

You left out active preamps.

Its possible to direct couple using tubes to create a balanced output. IME when you do this you have transparency and bandwidth on tap that's very hard to get any other way.

When running balanced I feel its important to support the balanced standard (AES48) since it prevents ground loops and minimizes cable interactions.

That initial statement was intended to address the different volume attenuator options, as discussed in the OP.  My current rig includes a passive resistive unit into an active buffer.  The icOn 4PRO is a passive preamp based on Slagle autoformers.  It so far seems to sound better alone than it does run into the buffer.

I doubt the guide on grounding and shielding connectors in active equipment presented in the form of the AES Standard 48-xxxx (2019 Draft Revised), applies to the icOn 4PRO, since it is a passive unit. Fortunately, I cannot detect any noise issues when using the icOn.

My concerns are functionality and sound quality, and right now both options offer similar functionality and pretty good sound quality, which is up there with the many good preamps I have owned (including a tricked out MP-3).