I also would rate the Merlin highly but I don't see it as a monitor. If you want a monitor, the best I have seen so far is made by High Emotion Audio.
http://www.highemotionaudio.comThe Pyra Bella 7. This speaker employs a unique tweeter that puts **all** dome tweeters to shame. It is much faster, with an extremely wide dispersion angle (in fact nearly 360 degrees as there is a rear-firing tweeter integrated into the tweeter array). So the sweet spot is really wide- almost as wide as the spacing between the speakers. Naturally the imaging is the 'best' regardless of make of speaker. What I mean by that is there is no speaker that excels in imaging compared to this speaker. High Emotion Audio was granted two patents on the technology of the tweeter.
The crossover and woofer are designed for a very seamless transition and the impedance curve is exceptionally flat so almost any tube amp can drive it as can transistors. The woofer itself is a custom design as it has to be very fast to keep up with the tweeter. The cabinet is quite dead and employs a rear-firing passive radiator. It takes about 40 hours to break in the speaker, once that is done it is quite honest down to 40Hz. The efficiency is about 92 db 1 watt/1 meter as best we can make out. It needs to be about 1 foot to 1 1/2 feet from the rear wall for best bass response. We use it on a Sound Anchors monitor stand.
We have used this speaker at our shop and also in the recording studio now for about 2 years. Not only is is faster and more detailed than the best planar speakers, it is also relaxed and you can listen to it all day. The tiniest nuances are revealed- you really need your electronic ducks to be in a row to take advantage of all this speaker offers, but in the studio we have relatively inexpensive transistor amps that we have used for monitor amps in a pinch, and its amazing how it still reveals very minor issues in the master tapes without the amp calling attention to itself at the same time. I attribute this to the slight phase angle and flat impedance curve- its not demanding of the amp!
They are not cheap by any means but there are not the most expensive either. If you really want the 'best' monitor out there, this is in fact the speaker you are looking for,