Saul. Note the Figure of speech Antimetabole (App-6) in this verse, and the Introversion of the subjects of this chapter.
Related Commentaries of 2 Samuel 3:1
2 Samuel 3:1
1 Now there was long war between the house of Saul and the house of David: but David waxed stronger and stronger, and the house of Saul waxed weaker and weaker.