It depends on the question of what's most important, doesn't it?
[This seems to be getting reasoned responses -- the best are the ones that answer all the questions. So I'll sticky it.--lambert]
That is, my vote -- which I haven't decided to give to anyone, though I'm leaning Green, since I'm in a solidly Blue state -- depends on a lot of factors, and how I weigh them. One thing: It's simply not true to say there are only "TWO" alternatives.
1. Is loyalty to the D most important to you? If yes, then vote for Obama. Period.
2. Is loyalty to democratic principles most important to you? If yes, then you are probably concerned with process violations at the RBC and in the caucuses. If yes, then you could withhold your vote for the top of the ticket, or vote for McCain.
3. Do you believe that voting for the best candidate for President is most important, and that [McCain|Obama] is that candidate? Then vote for [McCain|Obama]**.
4. Is the Democratic platform* most important to you, and do you believe that Obama will be able/is willing to carry it out? If yes, then vote for Obama.
5. Do you believe that expressing your preference for Hillary Clinton is most important? If yes, then if your state permits that, write in her name.
6. Do you believe that building alternatives to the [D|R] Party is most important? If yes, vote for that alternative party.
7. Do you believe that Obama deserves a popular mandate? If yes, vote for Obama.
8. Do you believe that Obama will be more effective in implementing Shock Doctrine policies than McCain? If yes, then vote for McCain.
9. Do you believe that getting rid of the current Democratic leadership is most important? If yes, then vote for McCain.
10. Do you believe that purging misogynists from the current Democratic leadership is most important? If yes, vote McCain.
11. Do you believe that you should vote for Obama because Hillary asked on his behalf? If yes, vote for Obama.
12. Do you believe that HR 676 (single payer) is most important? If so, vote for Obama; we're more likely to be able to force him to sign it than McCain. [Hat tip DCBlogger]
13. Do you believe that long-term progressive goals are most important? If yes, calculate your strategic position and vote accordingly [Hat tip paul_lukasiak]
And so on.
My state is reliably blue, so my vote won't affect the outcome, accept insofar as I deny Obama the perception of a popular mandate (see #6). In fact, I might conclude that's a good thing (see #7), and I also want to punish my thoroughly corrupt D establishment, so I just might vote Green.
But it's a long time 'til the election. I could still change my mind!
NOTE * Our expression of policies, and this year apparently driven from the grass roots, though I don't recall that aspect got a lot of play at the Convention. Readers?
NOTE ** There really is no point arguing that McCain is a force for evil, Republicans suck, McCain is a Republican and sucks too, Roe Roe Roe Roe Roe, et cetera. Again, the preamble to the D platform:
A great nation now demands that its leaders abandon the politics of partisan division ...
Meaning that, according to the Ds and Obama, a McCain choice is just as legitimate as an Obama choice. Now, you may not believe that, but Obama and his party do.