Favourite Raid per Expansion, including Vanilla.

[Revak]

Vanilla: Molten Core
TBC: Karazhan
WotLK: Ulduar
Cata: BWD (mainly b/c of the backstory to BWL)
MoP: HoF (mainly b/c of the theme) - I haven't enjoyed raiding much in MoP and all the raids have been pretty boring after a few runs. HoF struck me as the coolest the first time I went through it d/t the mantid theme and all that.

[Gum]

Classic: Zg/aq20.
TBC: The Eye, was pretty
WotlK: Naxx - i know it was easy, but nostalgia feels from vanilla.
Cata: Firelands
MoP: MsV - Pretty :>

[Caladia]

Vanilla: BWL
BC: BT
WotLK: ICC
Cata: BWD
MoP: SoO

[Deleted]

Vanilla: BWL, Molten Core.
BC: Karazhan, Black Temple.
WotLK: Ulduar, ICC.
Cata: Dragonsoul, Firelands.
MoP: SoO, ToT.

[jedijesse]

2. Karazhan
3. Icecrown Citadel
4. Bastion of Twilight

[Giscoicus]

Vanilla:Naxx (Got as far as the horsemen)
TBC: Sunwell
Wrath: Ulduar, but most were terrible
Cata: BoT by far. Sinestra was a fantastic fight, prefer it over any other.
Mists: this is hard. ToT felt moved but the bosses were ugh. I have to say Siege.

[Miley]

1. Naxx40- Didn't play then
2. Black Temple- Only beat Kara twice, gruul, mag, and pugged into a Daakara kill once.
3. ICC- wasn't in a good guild until late ulduar so I didn't do much of it. Loved ICC though
4. FL
5. ToT- I don't like MoP raids much. ToT beats SoO for me but I don't like either of them cause of how diverse the raid environments are and none of the fights seem connected.

[Therougetitan]

Vanilla: ZG
BC: Hyjal
Wrath: Ulduar
Cata: Firelands
MoP: SoO

[Forgettable]

1. Didn't play
2. Karahzan (Although I never had a chance to do TK / SSC / BT / SWP, so I don't honestly know)
3. ICC
4. Firelands
5. Haven't completed SoO yet, but it looks like that may be my answer due to guild drama in ToT. Both are great though.

[Tziva]

Classic: I guess ZG. I didn't do all the raids in vanilla, so my sample isn't complete.
BC: Karazhan
Wrath: ICC
Cata: Probably Firelands, but Bastion is close.
Mists: Throne

[Deleted]

Vanilla - Zul'Gurub purely because it was my first raid!
burning crusade - didn't raid mich in this one so it goes to Karazhan
WOTLK - tough call between ulduar and ICC, i think i'll give it to ICC, really fun raid, great atmosphere
Cata - Firelands is pretty cool, it looks awesome and the gear looks sweet!
M​oP - throne of thunder, not been fond of any of the raids so far really, but ToT was kind of nice

[MistsofBoredom]

Vanilla: Naxx 40
BC: Karazhan
Wrath: ICC
Cata: Bastion of Twilight
MoP: SoO

[geewhiz80]

1. Blackwing Lair (AQ40 was as far as I got)
2. Hyjal
3. Ulduar (favorite raid ever at this point)
4. Didn't raid at all in cata.
5. Siege of Orgrimmar

[Oratory]

1. Vanilla: Toss-up between Blackwing Lair and Zul'Gurub (although C'thun was my favorite boss of classic, I just hated the rest of AQ)
2. Burning Crusade: Black Temple
3. Wrath of the Lich King: Ulduar
4: Cataclysm: Firelands
5. Mists of Pandaria: Siege of Orgrimmar is pretty neat so far. ToT also good.

[spoon77]

I’m going to rate them two ways – one by encounters and the other by instance art/design

Vanilla:
Encounters: BWL. Slaying dragons in a huge group is was what first made WoW awesome to me
Artwork: Naxx

BC:
Encounters: Black Temple
Artwork: Karazhan. I know most people will say Sunwell, and it is amazing, but for what it is Karazhan is a spectacular design.

Wotlk:
Encounters: Ulduar
Artwork: Ulduar

Cata:
Encounters: A tie between BoT and Firelands
Artwork: Firelands

MoP
Encounters: Terrace*
Artwork: Terrace*

*I quit in 5.1.

[Serj Tankian]

1. Blackwing Lair
2. Sunwell Plateau
3. Ulduar
4. Firelands
5. Siege of Ogrimmar

[Deleted]

1. Didn't raid back then, I mostly lol'd around. I did do a few bosses in Naxx back in TBC though and in retrospect, Naxx was the most fun.
2. Black Temple
3. ICC
4. BWD or BoT. Or TotFW... Damn, can't make my mind up. Best fight was probably Halfus though, I'm a dps whore, so that fight really fit me.
5. SoO, best raid this game has had yet.

[Bullettime]

Classic: Blackwing Lair
BC: Karazhan
Wrath: Ulduar
Cataclysm: Toss up. Dragon Soul was better in terms of lore and lore contuinity in the dungeon. Firelands was better designed.
Mists: Siege of Orgrimmar

[Deleted]

1. didn't raid
2. Karazhan
3. Ulduar
4. Firelands
5. Siege of Orgrimmar

[Deleted]

1. BWL with AQ a close second
2. Didn't raid much but Karazhan was amazing for casual raiding
3. Didn't raid
4. Didn't raid
5. SoO