If the Democrats somehow nominated Dan Lipinski, Bart Stupak, or someone of the sort and the Republicans nominated a nut, Rand Paul, or John Huntsman, I'd probably vote for the Dem.
Why are Rand Paul and John Huntsman in the same category?
They are quite different from each other and only in the same category if that category is their appeal to me. My issues with either are completely different. With Rand Paul, I would be extremely hesitant to vote for him because he could support legalized drugs and/or prostitution. His economic views are also too extreme.
Huntsman I can't stand because he's been on what seems like a tirade against conservatives for the last couple years. Huntsman comes across as rude, condescending, and the type of person I cannot possibly vote for if I disagree with him on a single issue. Also the whole post-partisan schtick is obnoxious (though that might just be because everyone I know in real life who considers themselves "post-partisan" are so "post-partisan" they check all the boxes with the D's next to them).
Foreign policy isn't much of a consideration on my part, although Paul kind of scares me. I'd be concerned that if elected president he'd do something incredibly unpragmatic in the global arena and make a mess.
Hunstman is a weird one, because his record before the 2012 campaign was actually a pretty good one. He would have definitely beat Romney if he actually tried running in a Republican primary (as opposed to the MSNBC primary). I think his distaste for actual Republican voters is what did him in.