McCain stands absolutely no chance of winning the election. I say this now because it seems like he's finally starting to recognize that he's really not the front runner he used to think he was (hence why he's taken to criticizing Mitt Romney recently in an effort to put himself on a pedestal). The problem with McCain is that he became the likely Republican nomination too early, way back when Bush was still popular and relatively early on his term.
McCain painted himself as the same ol' same ol' plain vanilla Republican way back then, and has more or less stuck to that image (since his appearance on David Letterman, he has tried to convince the country he's a funny guy, but the only impression I've gotten is that he's tired and thinks he can slide into the nomination without enormous effort). But within the past year, sentiment in the country has changed; despite the boasting by major Republican candidates that they're all the next Reagan, the country wants someone a little more fresh.
A lot of Republicans don't like Giuliani because of his stance on things like abortion, but that just means that more Democrats would be willing to vote him into office. Giuliani stands a good chance of getting the nomination, I think; we'll see if he can get the general vote though.
He's my personal favorite. Even though he's starting to be known as the wishy washy candidate, he is the most solid and confident of any contender I've seen. Sometimes just looking and acting like a president (at least according to the country's expectations) is half the battle. I can envision Mitt Romney making awesome speeches and inspiring tons of confidence. The only thing I can see McCain doing is signing laws and vetoes and golfing on the weekends.