With the state of things I think it's very unlikely that Hillary Clinton will be the first female President. She has the faults of her husband, it's tough to know exactly where she stands on issues while feeling very political, but she lacks the undeniable charisma of Mr. Clinton. Whether you liked him or not, the man just oozed personality, and that's what a lot of Americans like in a candidate. The person matters just as much (if not more) than the politics, and that largely contributes to her high unfavorable ratings. In the grand scheme of things she seems less than electable, and a more generic but less polarizing Republican candidate could probably beat her.
Barak Obama seems to be another story, and almost the exact opposite. People really do like the man, he seems genuine, and even if you don't like his politics; he seems like a good guy and you can have an idea of where he stands. The fact that he's young and feels new also doesn't hurt. He seems fairly electable, but for one thing. This will sound awful, but it is true. If his name were Henry James or John Williams he would probably stand a significantly better chance in the general election. The nation wants a change, and a young, new, African American man isn't a bad place to start after two families controlling US politics for the last 20 years.
But the man's name is Barak Hussein Obama. That does make some people think twice. It isn't right, especially when you look into it, but the fact is that many Americans don't look into things, and all they have to hear is that and they might back off. And that really is a shame. But the want for change might make people overlook that.
Edwards is more of a generic candidate in my mind, he's fairly young and energetic, he has that going for him. He probably has a very good chance if he makes it to the general election, but with the current state of things that seems unlikely.
The Republican field to me seems thoroughly boring. Rudy Giuliani is an interesting character, and probably would have a very good chance in a general election due to how liberal he is socially but how he's viewed as tough and tied to national security issues. But, he's pretty liberally socially and his campaign has been a mess, so it seems unlikely that he'll become the Republican nominee (especially due to his lack of appeal to the religious in his party).
John McCain is back again, he seems like just a good guy as ever, but he also feels old. Not just in age, but we've seen him before in races and he feels more of an establishment character than some of the others at play.
Overall, this election is going to be pretty interesting, I think.