Personally, the most bitter Flyers for me would have to be (in no particular order):
1996 - to Florida. They were clicking on all cylinders heading into this series. They would have made the finals. Could they have beaten Colorado??? Well, they would have been clear underdogs. I don't think they would have won.
2000 - Blow 3-1 lead in East Finals to NJ. No words necessary. When Lindros was KO'd in game 7 it was obvious the era had ended. The rest of the game was anti-climatic. Any other franchise Lindros would have either won game 6 or game 7 with a heroic goal,,..... but not us. And they would have beaten Dallas in the finals.
2004 - Lost game East finals to Tampa - IMO they were the best team that season but injuries to the defense caught up with them, Why did Clarke decimate the depth at the trade deadline by moving Therien? This loss really hurt. In reality this marked the end of the run that began with the dawning of the Lindros era. This was their lost chance and they fell short. At different points during this run I was convinced they were winning the cup. I never had that feeling before or since. Hurt as bad as 87
I don't include something like 87,95, 2010 because I don't view those losses as bitter to the degrees of the above.
87 - it was a heroic effort. There was nothing bitter in losing to arguably the greatest team ever.
95 - bitter loss but there was the feeling of a great new era beginning and promises of glory in the near future. It seemed like a growing pain at the time.
2010 - bitter loss but losing to a dynasty,
1996 - losing to an inferior team that benefited from the tackle football rules
2000-2004 - game 7 losses in East Finals in which I maintain they win both finals if they make it.