I've sent my pics to 2 great and well-known surgeons for FFS but each of them gave me a different opinion about my chin. Both told me I lack chin projection. One told me I need sliding genioplasty while the other one told me I need a chin implant.

Which of these 2 options are generally better?

At first, it depends whether you are OK with implant in your chin or not. Sliding genioplasty is very invasive procedure (longer recovery) but at the same time this is the procedure to have if you want the best possible outcome, and the most natural result as possible. With implant the doctor can only do that much, and that may just be perfectly ideal for your chin and face shape, and you get away with less invasive and less expensive procedure.

Hiya

Perhaps you need a couple more opinions from other notable FFS surgeons.

I can attest to the invasiveness of a sliding genioplasty - it can take some weeks before you'll be able to eat properly, and the mental nerve (that's the nerve providing sensitivity to the chin and bottom lip) can suffer some trauma which can take many months to come right. After 3 months I am only now gradually getting back some sensitivity.

But since you come out of it with your natural bone and a couple of inert titanium screws, many consider this better than an implant.  I am very pleased with my result overall.

Dr Bart's website has a very good diagram of how they perform the access surgery for a sliding genioplasty. 

Hope this helps.
Julia