Definitely not Windhelm that's for certain and I highly doubt the likes of Markarth, Dawnstar and Winterhold would either. It's hard to say since some holds have hardly any Argo's in them. My guess is it would be a toss up between Riften, Falkreath and Morthal.
What do you think?
All Holds tend to have an issue with "outsiders". Riften, Solitude and Whiterun would probably be more open as they are or in the case of Riften were large on trading.
Solitude with close ties to the Empire is generally the first point of entry for any foreign merchants or dignitaries entering Skyrim.
Whiterun is the trade hub of the province, so they're used to a lot of passing merchant traffic and being the central location they would likely be a main stop when traveling across Skyrim.
Riften was once a merchant hub being close to Morrowind and Cyrodiil, except the city hasn't fully recovered from being burnt down by the citizens in an uprising against their Jarl 60 odd years ago.
Probably the Khajiit since they know what it feels like to be discriminated against; as well as being blocked to enter city walls. The argonians at the Windhelm docks can't even live inside the walls, and Khajiit caravans are not welcome inside too, and have to camp out in the snow to sell their wares at passersby. It's really sad, if you think about it. Comrades in misery, that's a bond that will never break.
Khajiit themselves aren't banned, only the khajiit caravans. Not exactly sad when you figure out many of them are unwelcome in Cyrodiil and Elsweyr due to problems with the law, they're also making a massive profit from smuggling and off the civil war by selling to both the Legion and Stormcloaks.