What is the best incision if I'm prone to keloid scars and interested in getting a breast augmentation? (Photo)

All scars risk becoming: hypertrophic (thicker), lighter or darker, wider, and rarely keloid.   The  risks depend on  your genetics and also the  location of the  scar.  Rarely have I seen problems with scars under the breast (and they are hidden unless you lift the breast)  Scars  around the areola  are visible just looking at the breast and in my experience can be  more problematic than the  fold scar.  You can however get  tattoo to darken a light scar.  There  are  many techniques  to help to improve scar healing from he technique to after surgery care: silicone tape, laser, steroid injections. I would suggest if  you still wish to go  ahead with  any elective surgery, with a history of poor scarring, you discuss with your  board certified plastic surgeon their philosophy and preference. 
Kindest regards,

For keloid formers, there is not a way to prevent keloids.  In general, the longer the scar or the greater the number of scars, the greater the chance for keloids. 
The only way for sure to avoid keloids is to avoid making an incision. Though the likelihood for developing keloids is low, there is no way to predict their appearance after surgery.
In the broad array of literature as it relates to keloid treatment, there is a global absence of definitive protocols in the management of keloid scars. As an author of "Scars and Scar Revision in Reoperative Plastic and Reconstructive Surgery", I am well versed in the potential treatment options.  One treatment may be helpful for one patient while another treatment may help another patient.
Most fair-skinned patients heal the incisions well, and the scars are barely visible at one year.  However, some patients can develop widened scars, hyperpigmented scars, hypertrophic scars, or keloid scars.  These may require multiple modalities to achieve the best results. 

Good morning!I find that the nipple incision heals almost invisibly by 12 weeks postop and has much less likelihood to form a hypertrophic scar when compared to a crease or armpit incision!