The bottom line is, you can't buy a mic, or anything else for that matter, based on the design alone. Each individual mic will be different. There is a giant difference between an AKG C-12 and a Neumann U-47, even though they are both top shelf tube mics. It is also obvious that there is a difference between those $5000 tube mics and the $200 ones that you get from Sam Ash.
Same goes for tube preamps vs. solid state. Same with tube compressors, etc... (in that case, the tube compressors are different because most of them use a photo-electric panel to control the reduction, but its that which maks it sound different, not the tube)