Thank you for an excellent question. As new technology develops, it is often difficult to determine the differences between them and which is used for whom. As for these two non-invasive treatments, they are quite different in how they work and what they treat.
-Ultherapy uses a focused ultrasound energy to work beneath the skin and on the deep layers of the skin. This causes a lifting effect for areas like the brows, cheeks, and neck. It also causes collagen rearrangement, which improves the skin. It does not improve the superficial aspects of the skin, so it is not a treatment for fine lines and wrinkles.
-Fraxel creates small holes in the skin which then produces tightening of the skin. It does not provide any lifting of the deeper structures, but does provide more superficial tightening of the skin.
The proper choice really depends on what aspects of your face you are hoping to improve upon. If it is tissue decent that you are hoping to treat, then Ultherapy is a better choice. If you are hoping to treat the more superficial aspects of your skin, then Fraxel may be best. Consulting with your plastic surgeon about the options is always the best way to determine the best option for you.
Best of luck with you face.