I still think Sisko is my favorite ST Character ever, but upon consideration, I also like Worf and Martok. Two "Quintessential" Klingons, in my book--If I were a Klingon, I'd probably aspire to being allowed to join Martok's house.
No - I think Gowron was the best Klingon ever. Gowron was a REAL Klingon.
Gowron is honorable - within the rules and bounds of Klingon society. It's clear that he recognizes those rules, takes them to heart, even he acts out of cynical self-interest.
Gowron is bold and and courageous. He's willing to take enormous personal and political risks to for glory and success - but that degree of personal courage does not translate into moral courage.
Like every warrior, Gowron eventually submits to hubris and madness. Such is a fitting and inevitable end to all warriors since the days of Greek drama.
Martok and Worf (as portrayed on DS9) were comic book characters. Gowron was the Klingon given life, how that way of thinking and acting actually works in reality and the sort of complex character it produces.