How do you choose?
2002 featured the biggest upset in my lifetime. Mclaren claiming innocence in his wwe clothesline on zednik. Zednik left the series, but the Bruins never won again. It was koivu coming back from cancer and scoring a beautiful go ahead goal in a game where the Habs were down 3-1 in the 3rd period. It was Gilmour turning back the clock.
2004 was another upset but not as big as 2002. Theodore shut out the Bruins in game 7 and ended up with more points than Joe Thornton. This was kovalev S's arrival to habs fans hearts after a slow start to the series. The Bruins had loaded up this year at the deadline and landed gonchar. The habs ousted them in the first round.
2008 felt a bit different because the Habs were the favourites this time around and were the #1 seed in the conference. They also mopped the Bruins in the regular season with an 8-0 record head to head. The series however went the distance and the habs won the deciding game by a score of 5-0 if I remember correctly. Streit scored a beauty in this one.
In 2014, the Habs upset the Bruins again, but this was probably a lesser upset than 2002 and 2004. The series had the typical hatred and physicality that you would expect from a bruins/habs series. I thought the Habs had something special that year and were probably headed to the finals prior to the price injury. The lucic/weise back and forth was pretty memorable, and subban was under their skin too.
Honorable mention to 2011. That looked like another huge upset with the Habs taking the Bruins to game 7 ot without Markov or Pacioretty all series.
I think I voted for 2008, but the more I think about it, 2002 had to have been the most emotional one.