Silicone implants have become extremely popular in the U.S. since they were re-introduced in 2006. In my current practice the vast majority of breast implants used in breast augmentations are silicone. This is for several reasons, first, of which is the natural feel and appearance that silicone implants can provide for patients. Silicone implants also tend to have less visible rippling than can be present with saline implants.
Many women who are very thin and go with larger implants can have rippling or a firm feels and looks to their breasts with saline implants. Many of my patients have switched from saline to silicone to have a more natural appearance or decrease their rippling. In general patients are extremely happy with silicone implants as they have a much softer and natural result with them.
In general I would wait at least six months before changing out your implants as this will give you time to have the swelling resolve. This gives the breasts a chance to heal before going through another surgery.