i duno if they are best, but they are certanly very good:
(using them for more then 3 years with various amps)
http://www.positive-feedback.com/Issue19/endlerattenuators.htm
or
http://www.icl.co.jp/audio/english/Model5/m5-1.htm
(using them for more then 3 years with various amps)
http://www.positive-feedback.com/Issue19/endlerattenuators.htm
or
http://www.icl.co.jp/audio/english/Model5/m5-1.htm