Well I am, as my father once so incisively put it, vacillating forthrightly!
I'm a political centrist. The only one of those in the race is Mr Sanders. The rest, including the other 'Democrat' in the race, are all right wing authoritarian nut jobs who are okay with the status quo, but for maybe a tweak or two.
Voting FOR Shillary as a vote against the Republican nominee strikes me viscerally as a distinction without enough difference to matter, although
@Fogdog was persuasive in his argument that she wouldn't be 'as bad'.
WHY THE FUCK WOULD I WANT TO VOTE FOR 'NOT AS BAD'?!
The Democratic party is just as bought and paid for as the Republican side, their job now is to continue enacting corporate friendly policies while saying they aren't as onerous as if the Republicans did it.
I'm just not sure I could live with myself if I supported that with my vote. I am far from alone; I keep running across anecdotal evidence of a mass movement within Democratic voters, especially younger ones, that if they can't vote for their beloved Bernie they will just stay home.
How big a movement this is I don't know... but it wouldn't have to be a very big proportion of the party to sink Mrs Clinton in the general, seeing how she's already polling just nose to nose with Ted Cruz.