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.