It depends on the procedure you and your surgeon decide is the best option for you.
Gastric Bypass (Roux-en-Y)
The stomach is divided, forming a small pouch which is connected to the intestine. The pouch is about the size of a golf ball, and results in the best weight loss, averaging 50-80% decrease in excess body weight and can help cure diabetes.
Vertical Sleeve Gastrectomy
This newest procedure is in between the bypass and band, in terms of effectiveness and safety. A section of the stomach is removed, which reduces stomach capacity without bypassing the intestines or causing gastrointestinal malabsorption. Weight loss is slower than gastric bypass; expect to lose 50-70% of excess body weight within twelve months after surgery.