I have tried RCA 12AX7 and enjoyed them in almost everything-got in a 1964 Bassman that was given to me. Many months back I found NOS Westinghouse 12AT7s and found they mellowed out my amps, and then got some NOS Sylvania 12AV7s and found they really mellow out my Vox AC4TV stack.
I recently got some used but "tested" (on a machine that looked as old as the tubes) EL84s. 1 RCA, and 1 Mullard "International." Up until this point I was using the stock Sovtek in my AC4. I tried the RCA and it had good headroom and punch, but when distorted it seemed to have a strange decay/fuzz. The Mullard seemed to have a tiny amount of this but sounded much smoother and like my Sovtek but without the dullness.
ANYWAY the point is, can a tube "test" good and still sound kinda weird/crappy? I know a place that has many NOS/used tubes that can be tested- somewhat- but I guess are some brands better than other as far as chance of getting a good "used" one?