Yeah, every set of tubes sound a bit different from the others, even from the same plant/year. That's what makes rolling so fun - finding YOUR pair(s). I probably purchased about 20 different sets from Herleen (Miniwatts, Valvo's, PQ's, SQ's) since I love the Herleen sound so much, and then narrowed it down to my two favorite pair - a set of e188cc Amperex PQ's I got from a guy in Greece, and the Valvo yellow-label CCa's. My humble advice is not to get caught up in brand, color, etc. If you really want to find YOUR tubes you've got to get a whole ****load of tubes at good prices when you find them, listen to them carefully and take notes, and then sell off the ones you like the least. I've been doing this bit-by-bit over the course of a year. In the end I've never lost money and have really got to know the tubes well. The other thing is to recognize that tubes that do not have at least 50+ hours of burn-in time will sound different once they are burned in (usually the highs tame down a bit), and we never REALLY quite know what we're getting. If you compare a non-burned-in set of Valvo's to the same tubes burned-in, it is like listening to two entirely different sets of tubes. So, if you really wanted to do it right, you would burn the tubes in yourself for 50+ hours so you know what they will ultimately sound like. Therefore, you have to be scientific in your comparisons - regardless of whether the seller says they are "NOS" or not. Build up a stock of tubes over time. Burn each pair in for 50+ hours, and then listen to the sets side-by-side, one after another, and back and forth. Do this for a few days and you should begin to hear the subtle differences everyone is talking about. The truest test, however, is a blind one - possible to do alone but much easier to do with someone else.
Cheers!