In other words, which POTUS elections did the (a) general American public at the time see as all candidates being poor options, and (b) do current historians and political scientists generally agree as them having poor candidates?
Hayes vs Tilden had neither candidate winning a majority of electoral votes and the election was basically decided by backroom deals.
https://en.m.wikipedia.org/wiki/1876_United_States_presidential_election
Progressives in 1968 thought that massive protests in the streets would push the Democrats to the Left.
It didn’t work.
For those wondering
A case could be made for 1976. The incumbent Gerald Ford was neither elected president nor vice president, and became VP after Agnew resigned before becoming president after Nixon’s resignation. He pardoned Nixon after the Watergate scandal, which was really unpopular with the American people. The challenger Jimmy Carter was an unknown before the Democratic primary, being the Governor of Georgia but was not seen as someone who would be more than that. It was a tight election with Carter barely beating Ford. It’s possible a stronger Democratic candidate would’ve won in a landslide, likewise a stronger Republican incumbent would’ve probably won easily.
I understand 1860 was pretty contentious.