@joeinid The answer to your question depends on your ears. Some guys like the 300b. I'm not a fan. I like 45 tubes. Others don't. The 2A3 is somewhere in between. If I had to pick the best sounding SET amp I ever heard it would probably be an AD1 amp built by Thomas Meyer. It was an extremely seductive sound.
If you want more information, this guy has a great website: http://www.glowinthedarkaudio.com/thoughts-opinions.html
If you want more information, this guy has a great website: http://www.glowinthedarkaudio.com/thoughts-opinions.html