I highly recommend dealers who scroupulously test there tubes for noise. Amongst them Upscale, Brent Jesse
(audiotubes) Tubeworld but very expensive, right here on Audiogon an exceptional dealer is Jim Sautter, I like Tubemonger as well. Although I haven't used him Andy at Vintage tube services consistently make his customers happy. If you want new production Jim McShane over on Audio Asylum will not sell you a bad tube.
Depends on your tastes really. For 12AX7 Old Mullards are great tubes that have a warm full tone. German tubes Telefunkens and Siemens tend to be very clean detailed and extended. I found the Old Tesla not JJ to be excellent no issue tubes. I have heard only good things about the Amperex but don't own them. Tungsram is another clean tube. BEL from India made some ARC stock tubes another decent tube.
For Modern Production much to my surprise Shuguang made a tube briefly then stopped it was called the C9 if you can get them try them crystalline sound. Otherwise the Tung Sol Re-issue is a fine all rounder.
For 12AU7s I found one outstanding variant that is well liked and in my view clearly a better tube it's the highly sought after 7316 only made by Amperex super imagery halography detail. They come up occasionally labeled for instrument makers like HP, Beckman. TVR2500 on Audio Asylum has them and is fair besides being a straight shooter. I use some Telefunken 802S intermittantly but they are unobtanium. Mullards have the house sound big tone very pleasant.
There is a basic dichotomy within old 5751s. Plenty has been written about these so do a search.Grey plates tend have a looser but prodigious bass in particular the GE triple mica. The older Blackplates are typically more refined and have taughter bass. The Sylvania Grey plate is a bit more constrained even the double mica. I use some Sylvania Gold Brand Grey plates 1960s for a little extra bass.
Most people like the older triple mica Blackplates from Sylvania which is impressive. These, GE Five Star, the RCA triple getter and Commands, and the rare Raytheon windmill getter (possibly top dog) are all great tubes. There is a fall of in quality in terms of sonics with recent production JANs from the 80s. Some seek out the early JAN and the early military tubes are fine. Curiously I haven't had a problem with microphonics
