Depends on what team you root for
In all seriousness, I think the Falcons loss was the 'worst'. A 3-1 series lead is nice, but is nowhere near as secure as a 25 point lead late in the third quarter
is should be. That Patriots comeback was something extraordinary; so many things had to go right for them just to force overtime (the first overtime in Super Bowl history I might add.)
The Indians loss hurt. But the city of Cleveland was coming off a championship a few months earlier, and as you noted, the Cubs were a really good team and healthier to boot.
The Warriors had their 73 win season but they had some issues themselves in the playoffs-- They struggled with the Thunder, Curry wasn't himself, Draymond Green acted like Draymond Green and got suspended for a key game, Bogut went down with injury in game 5 I believe, and the Cavs were clicking on all cylinders.
The Warriors were also coming off a championship the previous season. Given the talent level of that team, I suspect we'll see them in more Finals in the foreseeable future. Can we say the same about the Falcons? I mean, it could happen-- they are certainly positioned well, but they are not as stacked as the Warriors and NFL doesn't lend itself to continued dominance as much as the NBA does.