Best 12AU7?

Here are some of my favorites...

1956 Valvo Hamburg Long Plate w/ 45º D-Foil Getter & Medical Red Tip

1950/1/2 Philips Copenhagen Welded Plate 12AU7

1956/7/8 Mullard Blackburn Square Getter Long Plate w/ Medical Red Tip

Mullard Whyteleaf M8136 Box Plate with Mottled Glass

Siemens Silver Plate w/ Medical Red Tip

Mazda 3-Mica Short Grey Plate 

Genalex B749

GEC B329

Siemens E82CC Long Plate

Early 1950’s Landsdale Long Black Plate (possibly labeled for Philco)

Amperex 7316 Long Plate D-Getter or Short Plate Treble Clefs

Mullard Mitcham CV4003/6189 w/ Medical Red Tips

Brimar CV491 Long Plate

Brimar Long Black Plate with Medical Red Tip

Tung Sol Black Glass Mil Spec with Medical Red Tip

1955 Amperex Long Plate with 45º D Foil Getters

When Investigating 12AU7 Valves, the following is discovered!

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All 12AU7 tubes are rated Vhk=200V
All 5814A tubes are rated Vhk=100V.

Careful when substituting.

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Earlier references made to the 5841A, does not point out there is a Voltage Difference that could negatively impact on a Circuit. 

+ 1 Vintage Tube Services 

Didn’t see them listed, but for a new production tube..Ray Selects

(as mentioned previously, 'best" is system dependent)