Well I've been every race you can be (horde side). Here's my list:
(Female ofcourse)
Orc: best racials hands down, but their animations kinda suck!
Belf: racials are crap, look good in plate, good melee animations.
Troll: racial is okay for dps, don't look that great and animations are soso!
Goblin: decent racial, animations are pretty nice.
Ud: decent racial, great animations
Tauren: racial isn't that great and I just don't like them personally
I'm currently undead (female) atm and I actually like it a lot. Their racial isn't too bad for pve, considering you get feared sometimes in ToES & HoF. The heal isn't bad aswell if you're blood.
Ill probably be going goblin again here soon. I just love how they look!
female Orc has by far the best physical proportions and armor models. Also the Orc racials are pretty sweet.
I am looking forward to the Quality of Life changes to Unholy which is the spec i would prefer to be playing as DPS.
Lorewise, the first deathknights were Orcs (actually they were the souls of sacrificied Orc warlocks bound into human corpses)
My dk used to be a cute little gnome, but i hated how armor looked on the little bugger(except for the brutal gladiator's plate, if anyone is looking for some cool armor for theirs) And i finally changed it to male dwarf and I love it, bit restricted to helms where the beard shows, but it's great all the same, at least he can grow a beard and isn't like some silly blood elf.
i have a Blood Elf female.. it WAS a Goblin Female... but i race changed cause i got sick of looking at my Goblin...
For me Orc Male just looks beast for a Death Knight. The only downside of having a male Orc is that they look funny on horses and some other mounts.
Orc male for me as the armor looks sick, plus Blood Fury is always a little help on the DPS front
I will never roll anything other than a dwarf. Also stoneform and icebound fortitude stacked is a decent dmg reduction.
I'm about to get flamed but worgen female! I've been belf, undead, orc and human, soon I shall be worgen!
Human, Belf and Orc.
I prefer Draneai only because i like how some plates gear looks on then, but the greatest reason is because i love their death animation..., i remenber in TBC when i saw a death draneai with the Warglaives... the WG was in the ground just at her side not in her hand... i don't know why, but i found that so cool
But for Horde i prefer female orcs, they look really good with plate and they don't have HUGE shoulders like male orcs.... and they stand straight!
Horde: dark skinned BE female: Sylvanas deathdoll looks ftw!
Alliance: Male gnomes. Death midget with +Escape Artist + Exp on 1h swords is sweet.
Tauren DK here, they look the best in gear (with hidden helm)
Plus I just find their 2h Strike animation to be totally awesome, overhead smash! Their dual wield animation is also great.
I am considering a race change though as the downsides are you are targeted first in pvp, get stuck in doorways and on some terrain features, their casting animations are poor, and the racials feel useless given I don't main tank anything outside of 5 mans.
I love troll death knights (as my name suggests) loving their animations and trolls are by far my favorite race.
Orc all the way! Great DPS buffs for both the orc him and AND 5% pet increase if you ever go unholy! On the alliance I'd be a human for the free trinket.