Tier 8 and 10 DK sets are my favorites.
Tier 10 (Blue and Red variants) - Shaman
Tier 8 - Warlock, Mage, Shaman
CM sets - Mage
Sig by Pangcakes
Warlock: T1 (honestly ugly, but I'm nostalgic over it), T2, T4, T5
Deathknight: Naxx25 set, Ulduar25 Set, ICC25 Set
Priest: Dragon Soul Set.
The one during lich king with the little halo for priest tier.
Paladin t10 will always have a special place for me. Whatever people says, paladins looks good in dress!
The Dreadnaught gear is my all time favorite. Really badass set imo.
Paladin T6 is my main transmog atm, with ToTC boots that fit the colors (I've always hated the thick boot model).
Season 9 & 11 PvP gear look nice too, and S9 color scheme matches T13 very nicely.
Pally T12 (Firelands) heroic set isn't too bad either, once you get rid of the idiotic dress; especially with the red Midsummer flame tabard & fitting weapons it looks quite badass.
I really liked T4 Malorne set for Druids. Simple yet elegant, and wasn't overly colorful like a lot of gear in that era.
Judgement Paladin set remains a personal favourite. I wish they'd revamp the model though, it's so classic and iconic to the series. They even brought it back for Heroes of the Storm.
Because molten giant on shoulders.
I have mainly a fascination with the PvP gear sets for some reason:
Warrior - Ruthless Gladiator (DERP helmet!), Relentless Gladiator
Paladin - Wrathful Gladiator, Relentless Gladiator
Priest - Wrathful Gladiator, Ruthless Gladiator, Cataclysmic Gladiator (even with the derpy-looking helm)
Shaman - Wrathful Gladiator, Grievous Gladiator (the green one)
Paladin T2 and CM gear.
mage tier 2 and 3 was great. i like the blue and purple in them. For alliance tier9 also looked good - to bad im playing horde :P
overall mage tier sets are a bit boring in designs, however tier2+3 are some of my alltime favorits in any class
Warrior - Wrathful Gladiator, Challenge Mode, Earthen Warplate (Tier 11)
Paladin - Cataclysmic Gladiator, Judgement (Tier 2), Immolation (Tier 12), Challenge Mode
Death Knight - Malevolent Gladiator
Rogue - Bloodfang (Tier 2), Cataclysmic Gladiator, Challenge Mode
Monk - Challenge Mode, Tyrannical Gladiator
Druid - Eternal Blossom (Tier 14)
Priest - Sanctification (Tier 8), Avatar (Tier 5)
Mage - Heroic Firelord (Tier 11)
Warlock - Deathbringer (Tier 8), Sha-Skin (Tier 14), Challenge Mode
Shaman - Challenge Mode, Spiritwalker (Tier 13), Witch Doctor (Tier 15)
Hunter - Challenge Mode, Yaungol Slayer's (Tier 14)
Sorry, can't narrow down further, those are my favorites for each class OVerall as a Tier I'd say Challenge Mode wins. Most of them are great ^^
RIP The Mythic Dream
Since this is NOT posted in the transmog-forum, I'll say that my favorite tier set is ALWAYS top level tier, because it has the best stats..
Fact (because I say so): TBC > Legion > Cata > MoP > WoD = WotLK
My pet collection --> http://www.warcraftpets.com/collection/FuxieDK/
Shaman T10, and T13 (I think)
I like most Lock sets
I love a couple of the Druid sets from Wrath onward where they finally started looking like nature without looking ridiculous.
Paladin Tier 4. I fell in love with Maraad in The Burning Crusade cinematic and had the full tier set in BC on my Draenei paladin. The very first thing I did when they introduced transmog was go and farm them again (as well as matching non set items) along with the Hammer of the Naaru (for ret) and Aldori Legacy Defender/Edge of the Cosmos for Prot.
Overall, T6. Probably the only tier where all classes looked great.
Class specific: lock T5, warr T4 and priest T1 (with Bene/Aneth) are my fav.
DK: T8 and T10 (IMO Future sets need less bone and more plate)
Priest: T8, T10, T6, and T5
Paladin: T10 and T2
Warlock: T10 (IMO Future sets need less extravagance and more simplicity and hoods)
For my pally I've always loved the judgement and redemption armor, I do also love the H pally set from SoO, I sadly never got the redemption set, for my DK I love the starter sets and the MoP CM set.
Druid tier 7,5. Fantastic upgrade of the T3 model.