i've listened to ge, rca (brown base), several sylvanias, gold
aero and tung sol. they all provide a slightly different presentation--especially, resolution and frequency response and tonality.
my favorite is the rca because of its richness. the brimar is most balanced, in that it is on the neutral side, with a slight touch of warmth. it certainly provides enough detail, without emphasizng the treble.
i would like to hear a mullard someday.