The positives for saline are lower-cost. The negatives are increased firmness, more prominent rippling, and most significant is their tendency to completely deflate after rupture, demanding additional surgery.
The positives for silicone are their more natural softness and appearance, leakage does not result in a deflation therefore it does not demand secondary surgery. The negative is the additional cost of the silicone implant.
In my practice. I use approximately 98% silicone gel prostheses