This is not my area of expertise, but I do live 20 minutes away from a warehouse with 10 million tubes for sale. Their online home is here:
vacuumtubes.net (FAQ page too)
When researching "which tubes are best" for my pre's, I found a wide variety of answers, prices, etc... Some said Telefunkens are best. Some said telefunkens are crap and Amperex are best. Others said RCAs are just as good. You get the point.
I've had the best results from matched pairs of RCAs and Amperexs over the years. Your results, however, may be different. I tried a pair of Telefunkens but I think they were fakes. There are a LOT of fake Telefunkens and other sought after brands out there.
Find a dealer you can trust and stick with them. Try out a few different brands.
My tube retailer is great - they let me brouse their inventory, match the pairs right in front of me, always write the measurements on the box, and always give a fair price...can't ask for much more. I have no problem buying gear on Ebay, but not tubes unless it's from someone I know.
Hope this helps.