Novella and Short Story look like the toughest categories to me this year.
Novella discussion: I already spent hours agonizing over which I liked better between the Kij Johnson and the Mary Robinette Kowal for the Asimov's poll this year, and throw in the Objectively Best F&SF Novella, Ken "Writes-all-the-best-stories" Liu, and the Valente novella that I actually wasn't as impressed with, but all my friends and my girlfriend rave about, so that should get a bunch of votes. I haven't read the Grant but she's on the ballot twice, so there must at least be a dedicated fan base, and if it's brilliant, then Toughest Category Ever.
Short Story discussion: Paper Menagerie and Movement are like my two all-time favorite stories I've read in years. And I really think the award comes down to one or the other, although I loved Cartographer Wasps and "Shadow War of the Night Dragons: Book One: The Dead City: Prologue" (best title ever), and in other years they'd be more than worthy, and I'd probably like the Resnick more but I've given up too many tears to his stories in the past, and now I'm immune to his sentimentality.
Novels, on the other hand, Embassytown seems kind of inevitable. I mean I liked it but I think Miéville just seems like he and his style deserve to win lots of awards. I'm not talking about the contest of merit, because unlike the short fiction, I haven't read most of the novels yet, but I wouldn't bet on anything else if someone were to start an (illegal?) Hugo betting pool. 10:1 odds on Embassytown.