This is as much a thought-experiment as anything, to mark my joining the LLF and to perhaps stir up some debate in the comments.
Peter Hain has so far been neglected by the Labour left, and I can't see the reason for it. I have seen the strong supporters of John McDonnell pledge their support to Jon Cruddas, Harriet Harman, Hilary Benn and even Alan Johnson, so I would like to make the case for the most neglected "lefty" (by New Labour/Dep Leader contest standards) on the ballot.
First, he has something which Cruddas lacks: experience in the Cabinet and the respect amongst MPs which comes with making that position work. The personal credibility and influence which he has gained from his contribution to peace in Northern Ireland should not be underestimated. Moreover, the addition of a mandate from the Labour left and Unions would make him a force for Brown to reckon with on the left: his CV guarantees that he can't be totally ignored.
Second, he has a genuinely moral outlook: a commitment to genuine democracy at home and human rights abroad. If we are considering our nomination for Deputy Leader by virtue of what weight they have in the Cabinet for socialism and for good, I would suggest that Hain has it right. His adoption of the Alternative Vote system might jeopardise Labour's future electoral success by smashing the two-and-a-half party system, but it will energise and enfranchise the left as a whole, and it shows that he is willing to put people before party.
Thirdly, Peter Hain would genuinely be able to curb Brown's rightist tendencies in a way that no other candidate could. There is a strong statist consensus (right and left) in the Labour Party at the moment which I believe is extremely damaging to our popularity with the public. If Peter Hain could begin introducing a 'Libertarian' Socialist element to domestic policy, then the Party can finally leave behind Old Labour's unquestioning statism (sometimes at the expense of the people); leave behind New Labour's restriction of liberties and rolling-back of Old Labour's gains and begin a new movement to revitalise the grass-roots of the Labour Party.