The frontrunner candidate appears to be Mousavi, who was prime minister during the Iran-Iraq war. Ahmadinejad is under fierce criticism from his opponents for his handling of foreign policy and the economy. Should he lose tomorrow, the change in diplomatic tone of the Obama administration will be due some of the credit. Obama's repeated statement that he is willing to talk to regimes we disagree with, and his recent speech to the Muslim world, have undercut the rhetorical value of provocative talk from leaders like Ahmadinejad.
The Iranian public is on the receiving end of Obama's charm offensive and I suspect they are perceiving that perhaps there is a better way than Ahmadinejad's confrontational approach. This despite the fact that for the most part, Obama's foreign policy is largely Bush's foreign policy. What's different is how its being communicated and lets face it, the simple fact that Obama isn't Bush.
A change in direction relative to the US by Iran, a country with a serious role to play in the smooth withdrawal of US forces from Iraq and the Af-Pak theatre of operations, would be a major step forward. Should Ahmadinejad be replaced by a reformer candidate tomorrow, the Obama administration's change of diplomatic tone will have scored its first tangible win.