I have been using Gold Lion 12AU7's sourced from Ron Sheldon at Cryoset. Very linear sound and they last a vey long time! I buy all of my tubes there if Ron carries what I need. My Gold Lion GZ34 rectifier tube from Cryoset is a huge improvement over the stock Sovtek tube my gear came with.
I've read many accolades for Andy at Vintage Tube Services as well.
I've read many accolades for Andy at Vintage Tube Services as well.