I loved Heigan because of the dance :D
Loatheb,hands down, heroic or non.
Maexxna! Spider Love >8<
Anub-Arak although he was a pain in the butt to kill.
The Four Horsemen!
Hiegan, because of the lolz.
Favourite boss in Naxxramas is Kel'thuzad because of the lore and I think he is badass, 2nd favourite boss is Heigan because the quote from Naxxramas Hearhtstone is funny when he dies "I should have taken a shower" :D gj blizz you made me laugh.
Thaddius is my favorite because of how interesting his character is. The way the screams in naxxramas were actually people made into Thaddius, and when you kill him they stop, perhaps finally giving those people a final rest, was really cool.
Heroic Loatheb! :)
I love Loatheb!
If you're asking about Naxxrams in World of Warcraft, there are two favorite bosses: Instructor Razuvious (vanilla) and Sapphiron (WotLK).As for Hearthstone, I've only played against Anub'rekhan, so he'd have to be my (least) favorite.
Heroic Noth, loved this boss in the WoW game, and loved seeing him again.
For me Maexxna HC was the most fun boss to play
Thaddius, inbetween disconnects and failing positioning, he was a lot of fun.
Instructor Razuvious ... he gave us bad headache.
Heroiс Maexxna. Her returning hero power is... hard thing. :)
Heigan! DANCE DANCE DANCE
Thaddius was always great. Losing people to the jump and the fun of polarity shift made it a unique encounter.