Martok is my favorite Klingon as well. I think the DS9 writers and J. G. Hertzler did a great job of making him a real, believable, well-rounded Klingon character without turning him into a human with a funny forehead - as has happened with some other aliens.
Next to all his awesomeness late in the Dominion War, I think his best moments were during You Are Cordially Invited
. It was cool to get a glimpse into Klingon domestic life.