What is the difference between gummy bear implants and fat transfer augmentation?

Personally, I use fat transfer for medium fill- not for very large (over 400cc range) augmentation. Fat will fill in upper pole and address areas nicely provided you have adequate fat to use. I use Vaser ultrasound liposuction and specially process the fat for best results.Properly sized gel implants can give large and natural appearance and hold volume reliably.An exam and consultation with a plastic surgeon who performs these procedures is recommended to confirm you are a candidate as well as discuss your options and expectations.

Gummy bear implants are a variant of silicone implants. The difference being a form stable gel fill which imparts the anatomic shape. The gummy bear gel is the most cohesive/firm available. It is form stable and will hold a shape thus the shaped/gummy bear.
In my practice most patients will choose a smooth round device. When placed in the submuscular plane, the aesthetic differences are minimal. The downward pressure by the muscle across the upper pole of the round device forces it to assume a more tear drop appearance. Recent studies have shown that both patients and surgeons have difficulty distinguishing between the 2 implant types post-operatively. Additionally, shaped implants are more costly and have an increased risk of rotation.
Finally, although very rare, the few documented cases of BIA-ALCL (Breast Implant Associated Anaplastic Large Cell Lymphoma) have all been in cases of textured devices. Until more data is available many are shifting their practice back to smooth round devices.
Studies have shown most cannot tell the difference between the shaped and round devices when placed submuscular. In light of the added cost, larger incision, and BIA-ALCL risk...most will opt for round devices placed beneath the muscle.
Fat transfer is a more limiting and less consistent. Due to the variability of fat graft take/viability, what you see is not always what you get (6 months later). When considering fat transfer, less is more. Patients should not expect to achieve more than a 1/2-1 cup size increase (without multiple procedures).
In summary, implants can deliver a natural result (when appropriately sized). Fat transfer is less consistent but remains an option, especially if you are not seeking significant volume.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).