What is your favorite tube for a preamplifier ?

The 7193 (2C22) is the king of preamp tubes in my opinion. I converted my Supratek preamp to use these instead of 6SN7s; much crisper and clearer treble, with images that hover in the room with you.

I have used many the 6sn7 or 6sl7 are more bloomy not quite as accurate though the build of the preamp and coupling capacitors have a lot to say about the final sound also I use the 6h30 supertube in the special dD grade and I get plenty of soundstage quickness and musicality .I have the new Lector 0ohm preamp ,the beauty hear is that you have 4 choices on what kind of tubes you want to roll also please remember a good tube damper such as the Herbies he has several grades and a good power cord
and I strongly recommend using the better Silver fuses on all your gear your detail is clearly better if you gear is respectable.

6SN7s are nice as they have a low microphonic aspect. They are great in line stages and can handle a lot of current so wide bandwidth is easy. Although they have less gain than 6DJ8/6922s or 6H30s, the reduced microphonics compared to those tubes is profound- so it is easier to make a line section that is neutral with the 6SN7. Of course you can hand-pick the miniature tubes for low microphonics, but in doing the same for the 6SN7s the same advantage of the 6SN7 is realized.

Great suggestions so far.
If you are into DIY, 76 and 6J5 are two of the most linear tubes ever made.
The 6SN7 is a direct descendant of the 6J5.
Have fun!

Also agree with the 6SN7.

For me, so many 6922, 6H30, and 5687 based designs sound bright, glassy, and etched in the manner that many audiophiles often mistake for resolution or neutrality. I find many of them artificial and difficult to listen to for any length of time.