Best Score was a tough pick, but this one might be even more difficult.
The nominees for Best Adapted Screenplay are District 9, An Education, In The Loop, Precious, and Up In the Air. Normally, we look for Best Picture nominees, because Picture, Director, and Screenplay often go to the same film, but four of these five (all but In The Loop) are Best Picture contenders. Being a dark allegorical science fiction film, I don't think District 9 has a strong chance. The best contender, in my opinion, is Up In The Air, for its emphasis on character, great dialogue, and sweet-and-sour tone. An Education might upset, and there's a chance that Precious could rally support, but I think Up In the Air is just the sort of movie that wins here.
For Original Screenplay, we have The Hurt Locker, Inglourious Basterds, The Messenger, A Serious Man, and Up. Here we have three Best Picture nominees in the mix. The Hurt Locker is a great action film but is very episodic and The Messenger and A Serious Man are more subdued. My first instinct tells me that Up is the standout in this category. It has the most original screenplay in at least a decade with each bizarre and unlikely story element building up to a genuinely moving end. Up is, however an animated film, which historically fare poorly in the writing categories. That said, I'm going to pick Inglourious Basterds for the win. It has a brilliant screenplay boiling over with Tarantino's unique style of dialogue, but because most of it is in French, German, and Italian with English subtitles, audiences are compelled to pay more attention to the words and appreciate the language and subtlety of the script.