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

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.  

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

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.

It depends on what kind of results you are wanting to have and your amount of volume loss and laxity. Threads can lift and tighten saggy tissue, especially around the jawline and marionette lines.  These threads are going to penetrate through deeper layers of tissue.  This is not only going to improve your profile, but it is going to stimulate collagen and give you cellular rejuvenation that filler cannot give. 
However, if you have fat pad loss in the cheeks, you will also want filler to lift the mid and lower face as this causes dropping and laxity in the lower face/jowls. 
We recommend a consultation with one of our Master Injectors to determine how to obtain the best result for your anatomy.

Hello and thank you for your question.  There are many ways to address your concern but I highly recommend using PDO Threads for this.  PDO Threads typically have minimal down time, long lasting, natural looking results.  They do have limitations, but the best part is, more can always be added.  Having personally used them for my jowls, I can testify that I love my results.  Not only did it address the jowls, it helped with my marionette lines and nasolabial folds.  Hope this helps and best of luck from the Art of Ageless Aesthetics.