What is the best phono preamp you have heard?

Threshold fet-10/PC with e power supply.

The Graham Slee Era Gold MK V

The amount of separation between instruments, the dynamics and the speed with which it replicates the sounds breaths new life into recordings. The increased depth and width of the soundstage is mesmerizing and it is really something special to listen to.
It can be less than forgiving however for a recording that steps too far outside the bounds. It won't smooth that over.

The Robert Koda K 10 is now the best I have ever heard, but one must provide the best power cord (HFC Ultimate Reference Rhodium)and the best isolation (Star Sound Tech Apprentics platform on a good base.

I haven't heard a lot of different phono stages, but IMO, the Herron VTPH-2 seems to be the most uncolored unit. It is also very detailed and has excellent timing / transient coherence. Nice and natural dynamic snap. No stridency. I can find nothing wrong with it.

For the money, the Linn Uphorik MM/MC phone pre-amp.

It's extremely flexible & quiet and I'm using one in a non-Linn system with the EMT TSD15 SFL MC cart mounted on a Brinkmann Bardo / Origin Live Encounter anal;og setup.