What's best for longer lasting results? HIFU or fillers?

That's like comparing apples and oranges. HIFU will lift and tighten loose skin by stimulating collagen production. Fillers will replace lost volume. It's often best to use them both in combination to achieve optimal results. I would recommend an in-person consultation and evaluation with an experienced physician provider to have your concerns address and a treatment plan determined. Best wishes.

Thank you for your question payinggg.0. I understand your concern. Fillers are used to restore
lost volume in and enhance the appearance of the face. It is difficult to make an assessment without a
formal exam in the office where I can view the skin in multiple angles. However,
I hope the information provided here is useful.Sagging skin is a common concern. This occurs for two main reasons. First, naturally over time fat pads in the face get smaller and bony changes affect the structural support. This leads to downward movement of facial structures. At the same time collagen is lost, which leads to loose skin. With gravity facial structures also move downward which further contributes to the downward movement of the facial structures. For best results both of these changes can be address. By placing fillers such as Voluma in the upper cheeks, volume can be restored in the apple of the cheeks. This pulls up on the lower face. At the same time energy-based devises such as ultrasound, radiofrequency, and lasers can stimulate collagen formation to further pull the structures in the lower face upward. I find that a combination approach always works best.Please consult with a doctor for specific
recommendations.  Good luck!

Ultherapy effect skin and muscle tightening but filler can replace fat and collagen.
They have different job and they supplement each other. I use combination therapy to get the best result for my patients