The Four horsemen, I always liked that fight
Heroic Maexnna, while stressful, it was a really fun fight. It was also EXTREMELY satisfying to defeat.
Going to have to say Thaddius for favorite Naxx boss. His story is creepy and I loves it.
Thaddius was always my favorite boss, though his story was so tragic and sad. Made me feel bad for having to kill him in Naxxramas. Although Kel'Thuzad's reaction to the death of Mr. Bigglesworth was priceless. Who knew an undead Lich would care for a living Cat?
My favorite boss would have to be patchwerk simply because it was my first raid boss I had ever downed. Even though it was in naxx 2.0 I still remember how hard it was as a fresh level 80.
As annoying as Grand Widow Faerlina first seemed she now is now probably my favourite boss. She really got me to change strategies and deck builds.
For me it'll probably have to be Heigan the Unclean. That dance with 40 people back then was insane. Or, for those who had not-so-good computers back then, the designated 'stand in this corner to not die' groups. I wish Blizzard would bring back 40 man raids, even if it is hard to coordinate. Icecrown Citadel had the potential to be a 40 man raid, with the possibility of both Horde and Alliance to group together to fight the Lich King.
Kel Thuzad...so sad to meet him still human in Old Hillsbrad Foothills and so funny to "play" with his little cutie Mr Bigglesworth
I have to say I like the four Horseman the most. Doesn't get much better than hearing Thane Korth'azz yelling "To arms, ye roustabouts!"or "I'm gonna enjoy killin' these slack-jawed daffodils!
Heroic Maexxna, most challenging so far
Patchwerk was the best boss in Naxx. Tank dies then Patchwerk proceeds to one shot everyone while yelling "No more play?"
I'd have to say Heigan, I failed at the safety dance but it was so much fun!
Gluth. Because who doesn't love a giant zombie eating puppy? Plus people falling off the pipes before fight was pretty hilarious.
Kel'thuzad! Also always liked starting the raid by killing Mr. Bigglesworth, loved KT's reaction.
My favorite boss in naxx? Heigan, of course. This feeling when everyone fails safety dance...
Can't buy Plague Quarter yet so at this moment it must be Grand Widow Faerlina.
Heigan, love the dance.