In general, especially before the Treaty of Alliance, and the earlier neutral zone cease-fires, the Klingons thought very lowly of humanity.
However, fast-forward, in time to after the Treaty of Alliance, the Klingons likely would have access to human history. Would they have gained further respect for humanity after learning that WE had warriors much like theirs for many centuries (before we evolved to our technological advancement in the Federation), like Roman soldiers, Greek Spartans, or Samurais?
Yes the Federation has "warriors" of sorts, in combat-trained field officers for away missions and tactical officers and security officers on starships, but I'm referring to the Klingons' native passion for up-close and personal hand to hand combat with sharp blades and death. Humanity has essentially evolved beyond that by the time of the Federation.
So if a Klingon read about Sparta, Rome, or Imperial Japan, would that change their perspective on humanity quite a bit? Are there any episodes/scenes in any of the series/films/books where a Klingon mentions human warriors of old? I'm not asking for opinion-based answers. I'm asking for answers based upon 1) factual mentions in any Star Trek series/films/books, and 2) factual data based upon the Star Trek universe (memory alpha, any other resources).