6H30 tubes vs the others

The 6H30 is considered one of the least "tube" sounding tubes. That is a generalization, of course, but many people don’t like preamps that use it for that reason. Other people seek out preamps that use it. They think that it provides some of the beneficial aspects of tubes (e.g. more 3D imaging)  with less of what they consider tube colorations.

Audio Research also uses the 6H30 exclusively. I haven’t heard either company’s preamps but I think they probably sound different. You’re probably better off trying to figure out the house sound of different companies’ preamps and which might appeal to you. The best way to decide is to listen to different preamps, if you can, of course. I don’t get the opportunity to listen, so I’m like you. I try to figure out how they sound by what people write about them.

Also, I like to tube roll, so that keeps me away from the 6H30.

The military grade (DR NOS) 6H30 is a truly great tube. These were manufactured pre Y2K (year 2000) and are scarce and very expensive ($200 - $300 each). That said, the quality of current production is mediocre (sound and durability). There is a large market for high-quality 6H30s and I've mentioned this to the new Western Electric tube factory in Georgia (U.S.A.) (no reply).
The basic design of the 6H30 is ideal for audio.  

The basic design of the 6H30 is ideal for audio.  

The main issue with tubes like this (frame grid triodes; includes the 6DJ8) is microphonics, as they were not intended for audio. Linearity is good though.

Microphonics is the vibration of the tube’s glass, which introduces itself into the signal?
is that the purpose of the damper rings I see around some tubes? You’re saying it’s more of an issue on 6H30’s more than other tubes?

I've been using the 6H30, in pre-amps, amps and integrated amps for 20 years. never noticed any microphonic anomalies (used with and without tube dampers).