It is really going to hinge on how many of these - $$$$$$$$$$ - you have.
Mackie, Genelec, JBL, Yamaha,
and many other Studio Monitors are very high on the list though. Though given what you have said, I would avoid KRK
which tend to have a bit more bass emphasis. Yamaha
on the other hand are crystal clear, but a bit lean on bass, not to an extreme, and they are certainly worth considering.
Then we consider Size and how you will control the Monitors, by control the Monitor I mean what will be the source signal - Computer, CD, Other?
Most basic desktop monitors tend to be 5" and 5.25", so that's what I will focus on. These are going to run about $150 EACH -
while good are going to be expensive -
However, the JBL, Yamaha,
listed above are very good, and very reasonably priced.
There are things to consider. First these are not Computer Speakers, rather they are two identical speakers each with a volume control on the back on the assumption that you will set the volume once and never touch it again. The actually volume will be controlled by the source ... say a computer.
This is why your source matters; we need to determine how you will control the speakers.
Though not as flat and perfect as a Studio Monitor, these Edifier R2000DB
speakers have easily accessible controls. It also has Analog and Digital inputs, 100w, 5" bass driver, Bluetooth, Remote Control - $250/pair
At a bit more money, EMOTIVA Monitors
are worth considering -
The only way to refine our recommendations, it to have more information.
What is the Source of the Sound?
How much money can you realistically Spend?
Where will you be in proximity to the speakers? Is this on a desktop or some other arrangement?
Certainly you want reasonably flat response, but you seem to need far above that. You insist on perfectly flat response, can you explain that a little more? The more perfect the response, the more expensive the speakers.