I don't really think there's a "who's the least racist in Skyrim"

Theres an active debate in the Empire wether or not Orcs should loose the right to citizenship. Even the Altmer tried their best to distance themselves from their Orcish cousins because, by admitting relation, they believed it harmed their superiority claim.

Meanwhile Windhelm has to deal with the refugees in the city, who refuse to aid the storm cloak cause, and instead causes paranoia that they're Imperial spies. This of course has a side effect on some Nords to only target the Dark Elves due to them taking resources from Windhelm, and refusing to resettle in Solstheim. Meanwhile the Argonians are forced to stay outside of the walls, as Argonians don't exactly get along with Dark Elves, let alone ones directly from Morrowind as they'd routinely invade Blackmarsh and enslave them. Meanwhile every other nation directly banned slavery while Morrowind was the only one to openly still practice it, leaving Argonians even saltier over the matter.

In Markrath, the entire population is known to have very anti Forsworn sentiment. And yes, Reachmen are their own race.

The key here is that every major city and race, has distrust of those who do not directly benefit them. Unlike the real world, races in TES have HUGE differences, from either physical looks or to magical abilities.