Telefunken smooth plate- very nice inner detail, and smooth, open. The sovtek 12ax7lps are surprisingly good, sounding very much like the esteemed tele's, maybe better, but, one of mine suffered from infant mortality and they wasn't broken in yet. Rca's were giving me really nice results, having a real comlex texture and very detailed, but I didn't want to wear them (they aren't new, you know, I'm a man of humble means).
I have been having good results with 5751's. I'm using ge, and I understand that there are better one's out there. The 5751's tend to give it more of a neutral balance, which seems to let more detail come through, less bloominess, but you have to let them break in a bit, as they sound glary when you first put them in (that is exactly what I would expect from good tubes, though).
I did a thing-you might dig this. I turned mine into a passive. Why not? It's the perfect candidate, high quality rca jacks, switches, and most of all-a good attenuater. And the way I did it was real simple. I borrowed the tape in jacks, followed the wire to the tape switch, onsoldered them, and ran them to the attenuater, and CAREFULLY soldered them to the output of the attenuater, along with the outputs leading to the active circuit. the result is parallel leads to one set of rca's for passive operation, and the active and then out the regular rca output. Only problem is that they are reverse polarity, so every time you switch fram active to passive, you have to switch the polarity.
I highly recommend doing this, as if you are careful, there is no damage done and no sonic degragation to the active stage, and then you have the option of seeing how the passive sounds in the system. Join the debate.