I have heard it argued that 1976 was a poisoned chalice election. That is, that anyone who could have won that year would have almost inevitably seen his popularity erode due to stagflation, the Iranian Revolution, the general post-Watergate malaise, among many other issues that popped up, both foreign and domestic.
That said, given that this was a sensitive period of time, which candidate would have bungled things most severely, and most consistently across the board? Consider both the foreign and domestic policy challenges that laid in store for them.
Included in the poll is every candidate who won any state during the Democratic or Republican primary seasons that year, as well as Hubert Humphrey and Ted Kennedy, given that they were regarded as very strong potential candidates for the Democratic presidential nomination. I debated dropping Robert Byrd, as he seems to have run largely as a favorite son candidate for West Virginia, but kept him in to keep things interesting.
You are free to suggest other possibilities, and certainly there is someone out there who would have been unarguably worse than anyone included in the poll, but keep in mind that they need to plausibly win the 1976 election before doing any damage, or at least be a plausible addition to their party's ticket who could then assume the presidency in the event of a vacancy.