I’m looking to somewhat main 4 characters in Dragonflight, one for each armour type so as to be able to unlock most transmog.
For Plate I’m going with Paladin, for Mail it’s Hunter and for Leather it’s Druid. But I can’t make my mind up with Cloth.
I’ve never really mained a Cloth-class, and neither of the three appeals to me more than the other. So I figured I’d go by looks.
Almost all tmog is designed for humans imo, sex is up to you and mage mogs look great.
Female Blood/Void elf, although Blood elf more as the purple crap you get covered in in combat is awful.
elves. always
Kul Tiran Warrior Male in cloth armor is so Alpha
As someone said, pretty much all mogs are made for Human males (or is it type 1 now, not sure). So there’s that. BE for Horde or maybe VE work well to mostly for their similarity to Humans.
As for the class it really depends on what you want to play. Wanna play a healer? If yes, than Priest. Direct Healer? Holy Priest. Wierd Healer? Disc Priest. If you don’t wanna healer, then ask weater you want a wheelchair class? If not, than a Mage (Mages are almost wheel chair, but a step more mobile than Warlocks and Priests). You want a pet class? Destro Lock. DoT class? Affic Lock or Shadow Priest etc…
Draenei
We are simply fabolous in cloth slutmogs armour
for plate i’d say Kul tiran Male warrior, they are just perfect.
for mail i have a few options, but i would say Mag’har Male Shaman.
for leather nelf Male druid is just, Perfection. (if you use things such as Feral and Guardian.
for cloth Human male Mage or priest, both are preety standard but cool combos 
if you wanna get a bit more goofy thought,
any draenei rougue or Highmountain mage
Gnomes. Gnomes are superior looking in Cloth Armour compared to every other race. Only Dwarf Priests comes second.
This one:
Also, watching Goldshire burn is a nice bonus, isn’t it?
body type 1 mechagnome hunter
Destro? Demo is the pet spec.
Oops, typo. Yeah, Demo pets, Destro direct damage.
Blood/Void elves can even make a trash bag look good.
Humans work too.
and Female Draenei
Undead Holy Priest
Pretty much all armour, including cloth, looks perfect on draenei females. You’d almost think they were used as the model for everything by the devs, though they actually use human male. The exception is the tail messing with cloaks and hooves with boots, but since most cloth are robes that hide the legs, that shouldn’t bother you.
Priest is my answer.
Locks are ok
Mage set not that appealing except fews.
Belf or Velf, male or female.
Obviously they can’t be druids but why you want their god awful transmog is beyond me, still you then pick the next best thing: Female Nelf.
human female ofc.
Female draenei priest. We wear both robes and ninja leggings well. Shadow if you don’t mind everything being purple, disc or holy if you’d like to see your transmogs.