The Valve Drive is one of the few single-tube pre's that really does sound different with different tubes. The differences are usually subtle, but I did compare a bunch of tubes I had on hand when I got my Valve Drive. I found my notes from my testing (I recorded the Valve Drive with various tubes & then listened back later):
Svetlana 12ax7 very compressed & focused with medium overall output
Tung Sol 12ax7 lots of extra "air" and extended lows with "gritty" distortion characteristics
Sovtek 12ax7WA extra mids & very punchy, almost too punchy; very low noise floor
vintage RCA 7025 scooped mids with good lows- very clean, but lower output
Mesa ECC83 (probably Chinese) very high gain, loudest output, very smooth top end that gets smoother with more gain
GT 12ax7R edgy & a little brittle sounding, medium output
I greatly preferred the Tung Sol to the other tubes. It really gave my Valve Drive and almost Neve like top end. I use the pedal for very subtle always-on "hair" & the Tung Sol really nailed it!
For "crunchier" rock type tones, the Mesa ECC83 really shined, but that's not what I wanted out of the Valve Drive (I have other pedals for heavier od...).
Both the Tung Sol & old RCA provide killer clean tones if you want the Valve Drive functioning as a clean preamp. The Tung Sol has more going on, but the RCA was very "honest" sounding.
The stock Svetlana that came with the pedal was fine, but I really like how a couple of the other tubes really "opened" it up.
Of course, all of this is totally subjective.... But, I kept good notes & had an open mind during testing. As always, YMMV!