I think based on the likely numbers they will find it much harder than the Conservatives. The Conservatives will have more seats than Labour and will be the largest party. The LibDems have said they will work with the largest party.
Assuming nobody works with the SNP, I can't see how anyone other than Cameron will be PM.
Assuming the data is right, I cant see Cameron attempting to form a new government unless the others cant get their act together and formally announce something.
I see it as :
Tory + lib dem = short of a majority. As incumbent PM Cameron needs to go to the queen and ask her to invite someone to form a government. Unless Labour formally agree with the SNP I can't see why he would go to the queen and suggest she invites millband to form the next government.
So I suspect Cameron at that point would put forwards a queens speech, it would probably fail, I say probably because you never know what back room deals can happen. But assuming it fails the queen, or in reality a civil servant, will suggest the next person most likely to form a government. Obviously this would be miliband, who would probably manage a queens speech based on the anti-tory block.
Whats most worrying for the UK is Sturgeons insistence that SNP will not support ANY austerity the labour government wanted to apply. So take the first labour budget, it would need SNP or Tory support, ie backroom deals.
If they do go for austerity it would need to be strong enough to secure Tory support, if they change from their manifesto and decide to reject balancing the current defecit (call this austerity lite for want of something better) then they would secure the SNP support required.
Labour (or the Tories if they unlikely went into minority government) would probably end up at the end of the next parliament getting the same reception as the Lib dems do now even though they would hold quite a few seats. A minority Labour government will be a severely hamstrung one compared to their election manifesto and hence they will only be deemed to have broken most of their targets/commitments.
As far as they 2010 election was deemed a poison chalice, the 2015 looks more like a poison chalice with a nice side serving of ebola.