which 6sn7 gives the most air??

I suggest NOS USA made Amperex tubes, but they're hard to find (one came with my Dennis Had SEP amp, and I liked it so much I bought another one for backup)...I've recently scored a little pile of NOS Sylvania "chrome domes" that seem neutral and clear as a bell, assuming bells are clear. Sylvania NOS tubes aren't particularly expensive so there's that.

If the tubes have too much "air" they can cause a light draftyness in the listening area that will provoke old people into donning sweaters.