Mansun

I disagree here totally - on what basis have you made this judgement? Even from the logic that you have tried to use, the Mouth of Sauron appears to be the higher in rank by being the Lieutenant of Mordor & the Witch King only the Captain, but what evidence is there that he was more powerful than the Witch King? Gandalf never spoke of the Mouth of Sauron posing a threat to Middle Earth, yet was anxious of the Witch King & claimed him to be Sauron's greatest servant.

The Witch King was probably chosen as Captain as this was to be his forte - to drive the armies of Mordor into madness before the host of Gondor; he was certainly no political figure & was utterly corrupted by the Ring. The Mouth of Sauron was yet free of any such power, & through his cunning had grown into Sauron's favour. As somone said in an earlier post, the Mouth of Sauron was mainly a political figure for Sauron, to speak for him as best he could. If the throne of the Dark Lord was ever to become vacant, it would have been interesting to see if the Witch King would claim the title of Dark Lord ahead of the Mouth of Sauron?