One of the most transparent monitors I have heard is the S7 made by High Emotion Audio. Right now we are listening to the P7, which took longer to break in, but seems to work as well.
They both feature one of the fastest and most accurate tweeters in the industry, for which they have at least 2 patents pending. They are very honest to 40Hz.
They are equally easy to drive with tubes or transistors, and our amps drive them effortlessly.