Which classes might be more loyal to their ‘order’ for example if they had to choose between them and their Faction? Not as if they were at war but if they both needed assistance - who is the priority?
Would the Demon Hunters fight for the Illidari before the Alliance and Horde? I can see the Death Knights coming to the aid of the Ebon Blade.
Druids and Shaman seem to rally together for the better of Azeroth
Etc.
I’m sure it’s more of a person by person thing.
In the order over faction category most-all of the time I’d include:
In the 50/50 category where it could go either way
Faction over order I’d go:
And then a secret 4th category where its every man for themselves:
I remember wondering about this during inbetween Legion and BfA, with how unified the class halls were presented and how/why everyone would take sides in a new war… And then it was largely ignored from what I remember.
I don’t rp anymore but when I did, all of my DKs were secretly loyal to the lich king.
Agree with this list I was about to make my own but yeah this is what I would actually go for. Nice insight! It would have take me at least an hour to check to make sure I got it right IMO. 
EDIT: Oh I didn’t see Mages… You think if falls into conditional 50/50 category now that Dalaran is gone? I feel it does… but hey, depending how the story goes that can change too. (IMO)
I knew I was forgetting someone. I had them there in my mind, didnt make it to paper but are now! Even with Dalaran gone, the idea of the Kirin’tor or a neutral space to expand and learn magic as a concept is something Im sure they’d support with some like Blood Elves, Nightborne, Trolls (really just the horde tbh) feeling out of place and sticking more to their people/faction.
Paladins and Demon Hunters probably top the list… followed by Alliance of Lordaeron Mages given their history and characterisation in WC3. But not Mages as a whole.. generallly they are too individualistic for that.
Below that, I would place the rogues of Ravenholdt, mainly because its more like a Maggia.