What’s the best tube for a Sonic Frontiers SFL-1 preamp

Mullard 6201 I believe is what I used to run when I had a SFL 1, but that was sometime ago. Very nice preamp with the right tube and for the money. Sold the SFL 1 and moved to a ModWright SWL 9.0 SE which I liked much better. I recall the Mullards were what everyone was using and UpScale Audio recommended too which is where I think I purchased from. I remember the Mullard was much better than the stock tube if that helps.

SFL 1 lean side of neutral so my favorite was Amperex / Phillip Holland.  

I just picked up a mint SFL-1 last night , had a "new"  Brimar NOS AT7 but when I set it up I was pretty disappointed....dark, compressed sound it was bad.  Put a new JJ ECC81 in tonight and it sounds great.  

I was actually looking for a pre for my brother but he doesn't want to deal with tubes so I couldn't pass on it for $500....     its built like a tank.  

It will see duty in a second system but for now I am really digging it 

$500 is a steal for an SFL-1 - good for you. It’s a wonderful pre with the right tube to match your speakers and setup. Not really a JJ fan but I’m glad it’s working well for you. I never tried one in this pre. Not surprised by the Brimar but it’s a kinda naturally bright preamp so the previous owner more than likely tried to tame it with his speakers. Genalex and Mullard - can’t go wrong with either if you decide at some point to try something different. GL!

I think I'm going to order a Gold Lion 12AT7, but it looks like there are a lot of NOS of this variety around so I think I'll order a Mullard also

This unit is in place of my Conrad Johnson Classic 2SE right now and it sounds so good I think I'm going to leave it in the system for a little bit. 

Build quality on it is nice, I couldn't pass it up.    I wanted this preamp when it came out but I was newly married ,kid on the way so.........