San Francisco 49ers
Kyle Shanahan won’t like it but Jim Harbaugh was the best modern 49ers coach. It’s still wild that he quit the NFL to return to college football. But he revitalized the franchise after the disastrous Mike Singletary era. They won the NFC West twice and made it to the Super Bowl in 2012 (via Sports Illustrated).
We could choose Mike Singletary as their worst coach with all of the drama that he brought. But Dennis Erickson arguably has a darker legacy. He destroyed a decent roster and set in motion events that would hold the franchise for almost two decades. It took them a long time to recover from his ineptitude.