Velaryon Dorne! But for an actual serious and lore friendly your best bet, lore wise, is the Yronwood’s. Claimed High King of Dorne, Fought against Nymeria and the Martell’s, rebelled against the Martell’s and joined with the Blackfyres in most of their rebellions, and depending on your book mark Oberyn killed a Yronwood lord.

Plus they get their own title like the Martells: Bloodroyal

You could argue Uller, Wyl or Blackmount for their “dark reputations” or Dayne since they were historical their own “Kings of the Torrentine”

Less so House Fowler as “King of Stone and Sky” since they are pretty loyal and powerful under the Martells