Would it be better to have PDO threads or filler of the jaw line?

Using PDO threads is better than using liquid fillers such as juvederm because the threads are solid and retain the shape and structure while stimulating collagen formation, whereas, the liquid fillers have no form and tend to spread and lose their form.
Jowls can be improved significantly by using Instalift for pulling and collagen formation and PDO threads for filling to camouflage the jowls.  Surgical facelifts still give better and longer-lasting results. You must be seen by a plastic surgeon who can decide together with you what the best treatment for you is.

For a more defined jawline to strengthen your profile (and help prevent the dreaded jawline "jowl" sagging), we use injectable fillers like Revanesse Versa - a filler known to limit swelling and give subtle, soft enhancements - or Radiesse. Using a cannula to limit pain and swelling, we inject on the bone in strategic points to get more lift and shaping, resulting in a more contoured lower face and defined, structured jawline. I would suggest getting a formal evaluation with a facial sculpting expert. Best, Dr. Emer

Both are very temporary solutions. Although some report improvement after threads that last a year others only report an improvement lasting 3 months.  Jowls can sometimes be disguised by fillers by adding volume medial to the jowl.