The fact that McCain apparently seems happy with the health care status quo doesn't thrill me: I think when both blue collar guys and CEO's are screaming about it, and when you can point to other countries which spend less on health care but get better results, you've got strong signs that there's serious room for improvement. I'm also gravely disappointed with McCain's irresponsible public endorsement of the internet rumor (disproven by both the CDC and world health organizations) that childhood vaccines cause autism: this is about as bad as publicly claiming that donating blood puts you at risk for becoming infected with HIV. But other than that, I find a lot to like in his political record: it suggests someone who is making decisions based on what he sincerely believes is best for the country, even at the expense of his popularity within his party.
Clinton's high negatives remain a virtual deal-breaker for me: I'm very, very weary of politics where half the electorate loves the candidate and half the electorate despises the candidate, almost apart from whatever the candidate actually does.
I think for me this is how it will resolve: if Obama is the Democratic candidate, I'll vote for him regardless of who his running mate is. If Clinton is the Democratic nominee, then she'll probably get my vote only if Obama is her running mate, or if McCain picks as his running mate someone who would be wildly inappropriate for the Presidency (e.g. someone whose primary qualifications are religious rather than political or economic).