You can spend years developing your ear for your tube preference. With different amps it may also be different. Though mose preamp tubes will have some basic characteristics that will be common amongst them there are subtle differences that you will note. Some are brighter, darker, grainier, boxier, smoother, etc. It is your ear that will tell you what it is that you want. Again, even though you might get other people's opinions on their findings you will not be completely informed until you play the said selection in your amp. I would suggest taking any suggestions lightly then talk to your vendor and see if you can get what it is that you want. If at first you don't succeed there is always credit.... oops, did I say that? Really, tube taste can get really expensive because not only are you competing with other guitarists for your choice tubes but also you have others in the realms of tube audio (audiophiles) that are also on a search for tube tone. Fortunately for us, most of them will shun half of the tubes that we consider nice. That is why our current production tubes are still attainable. What makes it hard is that there is such a demand for NOS that because the supply is limited and the demand is so high that the tubes themselves will eventually become priceless. Currently some preamp tubes can be in the hundreds of dollars per piece. This is what I mean about market volatility and supply and demand with NOS. Though a preamp tube may last you a while it would be a good idea to get extras of the ones that you figure out that you like and keep them safe. For the most part in most guitar amps you can assume that your primary tone comes from V1. This is the place I would try to start the blueprinting process. You'll probably end up with a little assortment of tubes. This isn't a bad thing. Different tubes in different positions will often render different sounds. Sometimes this is enough to make your amp sound different enough that you may like it or dislike it. Take the time to learn your amp and your tubes if you plan on staying with a tube amp.