What are the best drop in subs for a 12AU7??

I've liked the Tungsram Industrial grade 12au7 from Hungary (dated 1971) available from A'gon member Tubemonger. Very quiet and detailed.

Thanks for all your input so far. The Mullards I own I bought several years ago on Agon and are labled as 12AU7. I do think they sound pretty good. I am pretty sure though that they are not 1960s Blackburns or anything that old. Probably 1970s possibly 1980s. I have to admit I haven't dug them out to check to see that they don't say 4003 somewhere on them. Any other suggestions? Keep them coming! Once again something that is not overly rare or expensive would be preferred. Thanks again!

You might try the very inexpensive (about 30 a pair) but remarkable jj ecc802's.. great balance between European warmth and American detail. 

I've been doing well with Gold Lion 12AU7s from Cryoset.  Very open, smooth sound and they stay quiet for a l o n g time.