In my ARC preamp I tried stock ARC supplied Sovtek tubes, then Upscale Audio EH6922 Platinum Grade and currently have Amperex made for Mullard in Holland(late 1960s).
Sovtek are a bit sterile sounding, a bit harsh on top.
But overall this was not as bad of a tube as some people describe it to be.
EH tubes are better than Sovtek with better bass, fuller midrange and with just a bit smoother highs. I think these tubes may work better if I listened mostly to classical music. EH tubes tend to sound a bit forward on some rock music recordings.
The Amperex/Mullard tubes beat both the Sovtek and EH. Highs are silky smooth. Midrange is full and vibrant. Bass is deep, powerfull, textured and well controlled. Soundstage is wider and deeper. Excellent tube overall for basically any type of music.
I think if my system was a lot more laid back in nature, then possibly the EH tubes could sound much better. But in my case, these 1960s Amperex/Mullard tubes are just a better choice.
Overall I am pretty happy with how my preamp responded to different tubes. Sometime in the future I plan to give NOS Amperex 7308 a try. See how it compares to my current tubes