I would argue that SL-1 with three dead was the nation’s worst accident.
Interesting argument - SL-1 vs TMI-2. More dead from SL-1, greater economic loss from TMI-2. Certainly, TMI-2 had a greater impact on the nuclear industry than SL-1 (SL-1 accident lessons - know your shutdown margin and practice good reactivity management). The lessons from TMI-2 were much farther ranging.