Siemens tubes are on the airy/ frequency extension side of the sound. The best are CCA E88CC grey plates. Those are silver plate and are not far from cheaper 1970s Siemens tubes with number printed on top of the glass. They are still very good if somebody is looking for that kind of airy presentration and are rated below Telefunkens i this application. For anybody interested find my previous post on tubes in WA2.
http://www.head-fi.org/t/494487/another-wa2-tube-roling-thread-my-findings-after-couple-months
And finally I've found 6AS7 brown cup/base but currently working too much so no time to roll them.
I think this has been already said many times about power tubes:
6080 - OK but do not stand out.
5998 for extension / a bit of body well balanced
7236 more like organic sound ( at least in my case )
6as7 for midrange sweetness
and brown base 6AS& suppose to be the sweetest of them all.
Be careful as a lot 5998 Chatham/Tungsol/Telefunken are in fact Russian
6H13C rebranded. Check the getter if it is located at the bottom. If looks like small UFO it is Russian, rectangle shape should be TungSol it is not rule of thumb but I've seen a lot of rebranded tubes especially that nowadays prices are going sky high. I remember buying 4 E88CC siemens A-Frame for 50Euros in 2005 now you are looking for 4 times the figure.
Also 6080 Telefunken I think are overrated for power tubes application in WA2 and in fact most of them if not all are not even Telefunken produced but rather GE.
For rectifier tubes I could not say the difference was huge but I liked RFT tubes best.