It should have a topic that is guaranteed to provoke controversy in at least a third of the incoming comments, but will also elicit enough agreement, both for the diary and for at least a third of the comments, so that it can be used as a MOJO builder; at least one cute animal wandering around for some reason; something that will at least potentially help democratic candidates get elected; a rant on propaganda, climate change, ALEC/the Koch brothers, the Tea Party, the NSA, guns, Republican obstruction, Democratic inadequacy, economic policy and/or theory, problems with HRs, malicious but undefined groups who are out to get Certain People, Trolls, and the partisan/dedicated behavior of the Daily Kos admin staff. Or, alternatively, it can be pure meta.
Whew. Now, I've got chutzpah, but not quite enough to try writing that. And besides, To be really ultimate, it also needs a) a recommend from Meteor Blades b) a sarcastic jbou comment c) a sardonic comment from Bob Johnson d) the perfect cartoon from JeklynHyde e) at least one great pie fight in the comments that slides down along the RH margin for at least a foot f) an appeal to the community
Here comes the appeal to the community: at least half of what makes a great diary is the comments, and so an Ultimate Daily Kos Diary has to be a community effort. What's your nomination for the Ultimate Daily Kos Diary of all time? What's your favorite comment ever? Even more, do you have a typical comment you tend to end up writing, or a comment you wish you could find a thread for? Have at it. If the threads start looking like the Great Orange Thingamajig/Doohicky/whatever, that's par for the course, too. Try to keep it classy - somebody may wind up quoting you.
And with a tip of the hat to Steve Goodman, I give you the Perfect Cowboy Song, to go along with it: