Following are my favorite combinations, for different reasons:
1. All around listening, very musical for all sorts of genre, this combination seems to please most everyone: Right side: NATIONAL UNION (black glass) -- Left side: NEOTRON or TUNG SOL round plates (both are pretty much the same construction).
2. For a darker sound with great bass, good for Rock, Texas Swing, Norteno, Reggae, the Harmonicats, and Jazz: Right side: SYLVANIA S6N7W (metal or black base: same construction) -- Left Side KEN RAD VT231 -- for a little less darkness substitute the Ken Rads with RAYTHEON 6SN7WGT or NEOTRON or TUNG SOL round plates work really good here as well.
3. Classical, very smooth throughout entire range: Right Side: SYLVANIA 6SN7W -- Left side: NATIONAL UNION (black glass)
4. Another classical, different from above, very pleasing: Right Side: BRIMAR CV1988 (black glass) -- Left side RAYTHEON 6SN7WGT (this combination can be switched from side to side)
For phono stage, have been very happy with the following: Back tubes: MULLARD CRYO CV4004/ECC83 -- Front tubes: TELEFUNKEN ECC83 gold pins from early '60s.