Since the FDA approved the new generation of silicone breast implants 4 years ago, patients have been asking me which is better. The short answer is that neither is better- they each have different pluses and minuses. The only one who can answer which one is better for you is you. After reading my opinion, it is my hope that you will be more informed and ready to make a good decision based on facts, not hype or internet gossip.
Saline filled breast implants have many benefits. They are less expensive, if they leak in your body, it is only salt water that leaks out which is 100% safe. Since they have a small valve to fill them and go in your body empty, the opening in your skin is smaller, and you can adjust the volume drop by drop to achieve more flexibility in matching the two sides. When you are 40, you will get a specialized mammogram, and there is no recommendation to exchange the implants unless a problem should occur. The negative is that if you have less than a B cup, they do not feel as natural to the touch, even though the appearance is the same.
Silicone gel implants have the advantage of feeling more natural in some cases, and can sometimes provide longer lasting projection in my experience. If I put a saline and a silicone implant in front of you and had you squeeze them, there is a striking difference in feel. When they are inside your body, behind breast tissue and muscle, the difference is most often impossible to detect. The patients who benefit most are those with less than a full B cup, and those who want very large implants. The minuses are a larger incision, the fact that the implants cost more, that they only come in limited sizes and cannot be adjusted drop by drop, and the FDA guidelines for follow up. They state that an MRI should be done at 3 years, and every 2 years after to check for a leak. They have also suggested that the implants be changed every 10 years. While some surgeons disagree with the guidelines, they are obligated to inform you of them. If they do not, my advice is to seek a different doctor.
So, the decision is yours. Make sure your doctor answers all of your questions, and that you feel confident and comfortable with him/her. A board certified plastic surgeon should offer you different options in where to hide the scar, implant styles and shapes, silicone versus saline, and show you pictures of women who look like you body shape and breast size wise with after photos you love. Good luck!