What filler is best for a chiseled sharp jawline? (Photo)

There are other excellent answers discussing the choice of fillers for defining the jawline.  Keep in mind that although Radiesse is an excellent filler for that purpose, since it is not hyaluronic acid-based, there is no quick and easy reversal agent if you do not like your result.
To add some color to the answer, neuromodulators (e.g. Botox, Dysport) may also play a role in defining the jawline either instead or or in addition to fillers.  Although it's impossible to know in your case without photographs or an in-person evaluation, Botox injections into the platysma muscle (which forms the bands in the neck and extends onto the jawline and face) can often improve the appearance of the neck and sharpen the transition between the jaw and neck.  Botox is easy, relatively less expensive, and a short-term (3-5 months) chance to see if it would help give you the results you desire.  
Best of luck!