Yeah, it can just be different, not better or worse. That's what Brent from Audio Tubes told me when I asked him about possible comparison in my amp between RCA black plates and Mullards, don't remember the exact model. And I decided not to get the Mullards since I liked the sound I had and didn't want it to be any warmer than it was. But someone else might've wanted exactly that, it would've been excellent sound too.
But for 12AX7 in the preamp my Mullards go nowhere.

