I'm assuming your bite and occlusion are normal; otherwise, an oral surgeon or orthodontist should complete their work first, and then you should get several opinions from board-certified plastic surgeons or facial plastic surgeons.
The chin implant surgery is easier to perform, less likely to have complications, and quicker to recover from. BTW, I recommend the submental incision (under the chin), since the intraoral incision has a higher risk of infection for which the implant has to be removed to cure the infection. The properly-performed and accurately-closed incision heals with an imperceptible scar in virtually all individuals. I would recommend a Flowers mandibular glove vertical tilt extended anatomic chin implant (size small or medium). Since this implant is a hard silicone elastomer (not soft and squishy like breast implants) and is placed in an exact-size pocket beneath the bone periosteum, it cannot shift when healed, and feels just like your own chin.
Sliding genioplasty has visible and palpable step-off where the bone is cut (despite the judicious use of bone dust and/or hydroxyapatite granules), and must heal like the (intentional) fracture it is. It's probably more expensive, and the claims of implants being "not natural" and "Your own bone is all-natural" is disingenuous--the cut bones must be held together by titanium plates and screws which are (guess what?) "not natural!"
Buccal fat pad removal is not recommended as it can yield a "hollow-cheek" Skeletor look--know what I mean? You will likely regret this later in life. Rather, conservative cheek implants (again, NOT placed via an intraoral route, but rather via lower eyelid incisions) may give you a more balanced and harmonious facial balance. In addition to the link below, see also my patient with cheek implants. Best wishes!