Novak & Murray stand 50-50 chance.
Sadly Fed has no chance of winning, though I wish he could. Agreed Fed won AO in just 2 years back in 2010, his performances at these slow courts in 2011 & 2012 were not so encouraging.
IMO Nadal is a wild card and his result is unpredictable. On one hand he is coming off a long injury break but on the other AO is the surface he clearly prefers than one at The Open.