I think the best possible outcome is Obama vs. McCain, for the sole reason that many, many conservatives deeply distrust McCain because of Rove's smear campaign in 2000. If they are presented with a choice between McCain and a non-Hillary democrat, some might choose to vote across party lines.
Also, I really, really do not support Hillary, and I hope she does not receive the Democratic nomination. Aside from the fact that she'll be fighting an uphill battle for Republican votes, she also has far more vested interests than Obama. I wouldn't be surprised if the Clinton administration was more corrupt than either the Obama administration or the McCain administration.