I've used a range of Stepped Att', with the DACT Brand being the most expensive.
A few lesser types than DACT, when used in my system put a lot of their traits into the end sonic, I recollect not much being an attraction.
I also use the Slagle AVC and know the Promethius TVC very well.
Both are in my view, as a Standalone an improvement over a Stepped Att'.
The AVC and TVC do add a hint of Richness, but that is probably the result of the windings. The overall presentation is where the design wins favour.
I have heard a Khozmo used as an upgrade VC and this was quite a substantial betterment.
On the same design Pre' as the one that had the Khozmo, I have heard it with the Prom' TVC as the VC. In comparisons the Khozmo was the one with the most attraction.
I have had Bespoke Stepped Att's made for my own pre' that is close in design to the pre's being referred to, as a result of the Khozmo.
It looks like systems are able to be quite influential on how the VC types are perceived.
There is also the digital VC designs, such as the 'Muses' that have been very much liked in user reports.