Who did Ammon say had a faith that was greater than that of any Nephite?

King Lamoni's wife

Ammon said unto her [the wife of King Lamoni]: Blessed art thou because of thy exceeding faith; I say unto thee, woman, there has not been such great faith among all the people of the Nephites. Alma 19:10

Because she believed him when he said that her husband (who appeared to be dead for several days and was beginning to stink) was still alive.