Amperex and Telefunken are considered top shelf tubes. There may be a better combination out there but I couldn't tell you what they would be. Some other PrimaLuna owners will probably chime in.
If you're willing to spend some money, call Kevin Deal at Upscale Audio. He is the PrimaLuna importer and has a large stock of NOS tubes. He is very knowledgeable about both. You can check out the Upscale Audio website to see what kind of prices we're talking about.