Do you have a favorite vacuum tube?

What type of tubes are you asking about; small signal tubes, octals, power tubes?
My favorite tubes for sonics are 6SN7GT... 1940s Tung Sol oval plates, RCA Greyglass, short bottle.
12AU7.. Brimar CV4003 boxplate, RCA blackplates, 1950s Mullard long plate square getter, Tung Sol 1940s blackglass, RCA 5814A Command Series.
12AX7... Brimar CV 4004, early Amperex/Philips Holland.

Also depends on the tube position such as gain, driver, phase inverter, cathode follower.

@2psyop (and anyone else interested in tubes), if you haven’t seen them already, watch the You Tube videos of Roger Modjeski’s talks at the Burning Amp Festival (from a number of different recent years), in which he goes into detail about tube design, construction, operation, etc. Roger has an enormous depth of tube knowledge, and dispels misconceptions and myths about them.

For my 12au7 utilizing preamp, my faves are Amperex 7316 PQ's, and for a more literal sound, Telefunken red tips....

I have some Amperex 7316s in my preamp now.  I had been away for a while and I had forgotten they were in there until this thread made me go check, but I have been thinking that my system is sounding good, so I have to agree with thecarpathian about the 7316s.

Had a C J Premier 11 amp with Sevtlanta 6550's.  I loved watching the blue violet plasma swirl around at night time.  It was surreal.  I'm

The Amperex 7316 is one of the best 12AU7s out there.
6SN7s are better than that though. 12AU7s, 6CG7s (also excellent) and 12BH7s are all based on 6SN7s (the 6CG7 and 12BH7 are literally 6SN7s in a miniature envelope; the 12AU7 is the same geometry but half-height), but for some reason the 6SN7 brings home the bacon the way the others don't.

Ditto on 6SN7GTBs as they're used in both my preamp (4) and my power amp (1). Faves are NOS Amperex, Sylvania, and RCA. However, the tubes that made the best impression on me relative to other tubes tried in this particular power amp are the Gold Lion KT77s. Surprising since I'd tried another brand of these and thought, meh...I'll buy another pair when the these get tired.