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

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 

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.........

Just ordered.a NOS Mullard 6201 hopefully that will sound better than the JJ, which isn't terrible but not my first choice

Those 6201 sound great .   I’m thinking about sending it to Chris at Parts Connexion but not sure which level to do