No doubt that Hillary is a seriously flawed candidate, but there are a lot of unquantifiable intangibles that her candidacy brings to the table:
-First credible female presidential candidate.
-Bubba's appeal on the stump.
-Boehner's inability to control House 'Pubs which will give swing state moderates (who decide every close election) pause about giving the GOP complete control.
-The Tea Party/Establishment divide within the GOP. A conservative blogger has already vowed to release Jeb's log-term mistress' name the day he formally declares his candidacy.
-An open seat and a crowded GOP primary field. Depending on who you believe, either the Perry or Huntsman campaign was the source of leaks that sunk Herman Cain. You're dealing with ruthless hyper-ambitious people who will do anything to win.
-Possibility of a disgruntled Tea Party primary loser running as an independent in the general election.
Hillary's best match up is vs Jeb since it cancels out the dynasty/retread factor. Mitt works too. Christie would probably piss off a majority of female voters debating Hillary. Walker (who just beat a female candidate in WI), Kasich, Rand, and maybe Rubio could beat Hillary under the right circumstances, but it certainly won't be a cakewalk despite Hillary's obvious flaws. Odds were definitely against McCain in 2008 and either Obama or Hillary would have beaten him, but Dennis Kucinich wouldn't have.