I think it would come as a major shock for any of them to go really, but I reckon Neighbours is in the most danger.
Neighbours survives in Australia pretty much only because of its popularity in the UK. When the next contract renewal thing with fremantle comes up, I think in 2016, I don't think Five will be willing to pay anywhere NEAR as much as they did when they first got it (300 million IIRC). When Five bought the rights from the BBC, Neighbours was a program watched by 5 million average, whereas now it's flittering just over/ under 1 million and without going back and checking all the ratings for this year, THIS WEEK it only scraped into channel 5's top 10. So it's popularity here seems to be dwindling too.
I suppose given what little attention it seems receive, Doctors might also come under threat at some point.