Anyone but McIlroy. Whilst his performance at the US Open will be the reasoning for him opening as favourite, golf doesn't usually work that way except for Tiger in his pomp. McIlroy could become every bit as good as Tiger but he isn't yet.
I have a feeling Donald will break his duck here, he's been on form, he won at the Scottish Open last week and his consistency over the past few months has been unreal.
Someone mentioned Garcia, the only reason I'd bet on Garcia would be to lay him. He can't putt and if you can't putt you won't win an Open.
I've no idea what odds Kuchar is but he's been over here for a bit acclimatising and put in a solid performance for a Yank at the Scottish Open, and is comfortably in the Top 10. He would be my "outsider".
EDIT: Kuchar is 41's on Betfair.