As much as I would like Rudd to win, there is no way that's gonna happen (in this ballot anyway). Given the current hung parliament situation, the majority of independents have indicated that they will break off deals with Labor if Rudd wins. Hence, even if Rudd was to miraculously succeed in the ballot, it is likely that Labor will risk losing government majority as the independents will withdraw their support and move to the Liberal side to form a majority leading to an Abbott government. If this majority does not work out, it would potentially force an early election. This outcome is the last thing Labor needs under shitty poll results.
If the independents decide to still back Labor then given his popularity with the public, then it will be a brighter outlook but this situation is highly unlikely.
Consequently, the least risky outcome for the Labor party would be to back Gillard. That way at least they will still hold government until the next election in 2013 and hope to redeem their poor polling in a year's time (which seems unlikely at the moment).
In summary, either way Labor is screwed...