I think draenei. They’re the go-to Light race and also ironically have one of the only canonical shadow priest orders; The Auchenai.
Kind of the complete priest package.
Forsaken have (had?) The cult of forgotten shadow but I’m not sure how central that is to the lore these days. They work really well as shadow and an argument can be made for discipline. But Holy doesn’t suit them at all.
Holy crap, had to google it. Forgot all about that, I’m sorry little blood elves, I left you out it.
The correct answer is always Draenei. I wouldn’t be biased at all.
It’s absolutely not classic, but pick dracthyr, you can thank me later.
Human. While every other race might have something that is priest like when it comes to an actual priest class, it’s based on the light and that leads back to the humans of the cathedral district in stormwind.
Oh I know, that’s why I play Draenei. BRF’s tier set is called the “soul priest raiment” which is supposed to be what an Auchenai priest would wear. Draenei has surprisingly strong lore for shadow priest.
Any Race says Priest, it’s a very easy word to say 
Draenei, if only cause technically they have centuries of experience more being Priests than Humans, who weren’t even really what they are now when the Draenei were at their peak with the Naaru and Light governing their society.
After that Troll/Night Elf, who are only slightly younger as Priests of Loa and Elune, and then finally Humans.
Those extra spicy Space Goats
One of the more rare races to be anything actually. Might be a reason for that.
There is somehow about as many Pandas between both factions as there are Vulpera…and Vulpera required an unlock.
Yeah who can’t say pry-est?
Human /10char
Pried…Priory…Prestidigitation…Presumably…Prickmedainties…
Nope, can’t do it.
Human.
Draenei second.
Horde is probably Undead, ironically.
For my favorite class (lock) i associate it most with Orc. Draenei if youre going Eredar theme. But personally i favor elves and trolls.
Alliance wise:
Original dwarf priests are my favorite. Love their casting animations and just the vibe of being a pious dwarf. For Holy/Disc.
For shadow, Void Elf just fits the theme perfectly.
Kyrian but they aren’t playable.
As for me, Nelf Hunter, also ironically my first trial character at the end of WoD/early Legion before I came back full sub at the end of Legion.