They're all pretty much jerks.
The Forsworn are basically being forced under duress to do the Silver-Bloods' dirty work, so you can think of them as the underdogs, but they are still bad guys. Thanor Silver-Blood uses the Forsworn hatred of Nords as a cover for the murders he has them do, but the hatred is still real (which is why it makes a good cover). Madanach would be doing his best to kill Nords whether Thanor coerced him to or not.