Depends on what your willing to spend, and if new or used. Used CAT preamps are pretty hard to beat, and can be had at the $2k range used, or thereabouts, Also, if you can find a used Sonic Frontiers Line 2 or better, they do very well also, and are aound $1200 range or more on the used market). The Audio Research LS22 i believe is also a pretty good piece for the money, and is also an older used hunt.
You may also give the much talked about Audible Illusions Mod 3A a shot, as it's a good preamp on it's own, yes, and around $1200 used or less. All these preamps are pretty much class A rated, or close. System dependancy always makes a difference, and you'll justhave to try with your gear! Good luck