The "BEST" pre-amp is the one that sounds the best TO YOU in your system IN YOUR ROOM, period.
If you have a good dealer, he or she will loan you as many as you like until you make a decision.
Personally, it is my belief that the company most praised for its pre-amps over the last 40 years or so is Audio Research Corporation. You might want to try a few of theirs to see if one of them works for YOU.
If not, there are some others that also have good reputations. In the end, the one that most pleases YOU IN YOUR ROOM is the one to buy.
Do not settle for anything less, please.
Cheers!