As I have written in answering a related question, Botox injection just below the eyebrow can create a lifting of the brow by relaxing the muscles that normally pull or hold the brow down. This so-called "chemical browlift" is most commonly used to lift the outer third of the brow but can be used along its entire length. From an aesthetic perspective, the brow arch should peak between the middle and outer thirds. This Botox effect will only last 4-5 months, whereas a surgical browlift should last many years. Thermage works by tightening skin due to application of high energy waves. Generally speaking, Thermage has been used more frequently in other areas of the body, not around the eyes or for browlifting, and I don't think the subtle skin tightening would withstand the normal downward muscular pull in that area. My preference would be for either the Botox treatment or surgery, depending on your degree of brow sagging.