This one is easy:
1. Philadelphia Spectrum - Loud, nasty and filled with a bunch of mean-spirited players and fans who are out for blood and always seem to be in a foul mood. I've seen fans bloodied numerous times and I've seen Flyers teams in the 70s and 80s literally scare other teams off the ice. Heck, I've even seen a 10 year old girl with a Crosby jersey get a full beer dumped on her in Philly. Those fans are out of hand at times.
2. Boston Garden - Similar to the Spectrum and even more compact. The Boston crowd isn't as insane as the Philly crowd but were pretty darn close back in the day. The old garden was notorious for nasty games involving the Big Bad Bruins.
3. Chicago Stadium - From the anthem to the organ to the maniacs screaming on the top of their lungs, the Chicago Stadium was a hard building for visiting teams to play in. From a noise-perspective, only the Montreal Forum rivals this place. The fans were way more behaved than the ones in Philly, Boston and New York.
4. Montreal Forum - Extremely loud and packed with the most passionate fans in NHL history. The volume level, media frenzy and mystique made the Forum very intimidating, but it wasn't "dangerous" like Philly.
5. Madison Square Garden - The Garden is the best arena in the United States to see a hockey game. It's old school and the fans know their hockey. Despite being a "matinee" city, the fans are serious hockey fans and have major attitude - especially back in the day. The building is loud, passionate and NY fans have their own rep for being pretty darn nasty, although not as bad as Philly or Boston.