I have an overbite (and possibly overjet). Chin implant or Genioplasty? (photo)

Happy new year. First of all, you don't have a significant weakness of your jaw or occlusion problem based upon your photos or imaging. Hollowing in the cheek is evident as is some fullness under your chin on the neck. These can be addressed readily
That being said, if you want to adjust your jawline there are several options. A chin implant will be great long term, can be done in the office with local anesthesia, and is very safe. A genioplasty includes a substantial amount of implants as well (metal screws, etc) so the silicone implant is overall better in my opinion.
Your neck could be treated with a deep neck contouring and the cheeks with either implants or filler.