I need to replace my E34 tube on my Audio Aero Amp

I personally like the JJ tubes, but there are just as many out here who prefer the Svetlana. The two have different sounds, it's a question as to which are more suited to you.

Svetlana are warmer and sunnier, JJ are more forward and open. Both are excellent so you really can't lose. I don't know what EH sound like, but you'll probably have some recommend those as well.

The current production Svetlana branded tube is not a real Svetlana. It is made by Sovtek and is not very good. The original Svetlana factory is now selling under the name SED with a Winged C logo. This is a great EL34-E34L. Almost as good as some of the very expensive NOS tubes. I think it is considerably better than the JJ version. Again, the real Svetlana tubes are now branded SED-Winged C

Now it's time to learn tube rolling! All EL34's sound different. Personally, I feel that vintage Mullards are best followed by telefunken. NOS Siemans can be nice too and a little less money. I agree with infinitebaffle about svetlana's. The Shuguangs are nice but a little too "soft/laid back". I got my hands on some NOS Groove tubes and am amazed. Older US made EL34's can be great.
You need to decide on what means most to you: detail, cranking rock, tubey sound, just plain accurate, bright.... and then start looking.
Try:
upscaleaudio.com, tubesandmore.com, jeffssoundvalues.com, thetubestore.com, tubeworld.com(just to window shop-too pricey).

I'm currently using the JJ's E34L blue tubes and am very happy with them on my VAC Avatar after comparing to EH and Golden Dragon (stock). The EH tubes were too warm for my taste and the soundstage narrowed significantly. The Golden Dragons were great and I would be just as happy keeping them, but the JJ E34L blue's have better bass extentsion and slightly better dynamics. That's why they are staying.

If you are happy with the sound with the E34L's and can isolate them to a particular (bad) tube, why not just go get a new pair? IMHO, short of spending the big bucks on NOS or other mega-dollar tubes, JJ is really a pretty good choice for the price. You can try either he regular JJ EL34's or the JJ blue E34L, with the latter being about $20 more for a match quad.

For reference, you can also get a back copy of the Valley Tube magazine (spelling?). I believe they had an issues specifically on EL34's.

Infinitebaffle is correct. I had been using the 'new' Svetlana's, recently switched to the SED's, harmonically richer, more transparent. SED's are the way to go.