More of me rattling off the categories that I have seen.
What Will and Should Win: Slumdog Millionaire (edited by Chris Dickens)
However you may consider Slumdog as a true Oscar contender, you should at least admire Dickens' amazing editing. He is usually thrown bad, less vitalizing editing jobs, but here, his style fits with Danny Boyle's, and the result is a masterpiece of masterful cuts.
The other nominees:
The Dark Knight (edited by Lee Smith)
How can you deny the full-fledged power of the biggest, highest grossing movie of the year? It really wouldn't have worked for me with choppy editing, and Smith, the veteran craftsman who cut Master and Commander, shows he really can do his craft well.
Milk (edited by Elliot Graham)
Not necessarily such a editing showcase, Milk still is pretty polished from the cutting point of view. Graham creates some desperation with his skills, especially in the closing scenes of the film. It's a job well done, definitely. (ed. I now remember there is some good archival footage editing, too).
The Curious Case of Benjamin Button (edited by Kirk Baxter and Angus Wall)
As a film, it's uneven. Technically, though, "Button" has redeeming features. It's well-edited, especially in those battle scenes. Though I don't support the decision to edit it not in chronological order, that's more of Fincher's call than that of Baxter and Wall, so I praise them somewhat.
Frost/Nixon (edited by Mike Hill and Dan Hanley)
Everything about this movie screams uninspired, and the editing isn't much different. The decisions in the editing room were pretty typical, since I've seen this many times before. Hill and Hanley, Howard regulars, won rightfully for "Apollo 13," but they shouldn't win for their lackluster work here.