For starters, I'm personnally opposed to Hillary Clinton running for president in 20o8. I've nothing against her, but she made a promise to the New York voters to be their Senator for another six years - and New Yorker accepted her promise by re-electing her for another six years. I don't approve of her being Senator for eight years and then being president.
I mean, it looks bad. The last person to be New York Senator before being President and after a former White House post was Richard Nixon. Is Hillary trying to pull a Richard Nixon maneuver - it really looks like it.
Then, over the past half century we've had Republican Presidents almost sixty percent of the time (seven terms) and we've had Democrat presidents over fourty percent of the time (five terms). Right now we're just trading out years of W for years of Eisenhower.
In the short term we've had six years of W and will be getting two more. That's preceded by eight years of Clinton. I really think that America is going to elect another Republican president in 2008.
So then you're left with the Clinton / Obama scenario. If either of them with the Democratic nomination I think they are going to loose - and right now they are the four-hundred pound gorillas.
Likewise I think that if McCain runs for president he's a shoe-in for the Republican nomination. I'd vote for him. The only big question is whether or not he'll run - he's getting up-there in terms of age.
Being a moderate, I'd sooner vote for a Moderate or Liberal Republican rather than a Liberal Democrat.