While it would be difficult for someone to tell you whether you would be best suited to have implants placed over or under the muscle without seeing you, there are a few things to consider that may help you. Currently, more implants are being place under the muscle, than over the muscle if you look at breast augmentations across the board. And, because of this, many people have heard that it is better to go under the muscle. This is, in fact, true for many women. However, some women are good candidates to have the implants placed on top of the muscle. Factors that wll allow a good result when going on top of the muscle include, a moderate amount of breast tissue, the use of silicone implants, and some tissue looseness without true sagging.
One of the major advantages of placing the implants under the muscle is how the upper pole of the breast will look in women with very little breast tissue. In these women, the muscle helps give a better slope to this area, and makes it look less like there is an implant. When you have a moderate amount of breast tissue, as in a B or C cup, the breast tissue itself will give the coverage needed to look natural, and the advantage of going under the muscle is not necessarily needed.
Silicone implants generally do better on top of the muscle than saline implants. This is not to say that saline implants cannot be placed under the muscle, becaue they can be. However, silicone, due to its compliance and softness, will tend to do a bit better than saline on top of the muscle. (Once again, the more breast tissue present, the better saline implants will look and feel on top of the muscle.)
The last issue is tissue looseness. It is a mistake to think that placing an implant on top of the muscle will be a replacement for a breast lift. If you have sagging, a breast lift will almost always be needed for the best results. But if there is some looseness to the tissue without sagging, going on top of the muscle may give a bit better filing of the soft tissue envelope. However, this may mean that the implants are slightly lower, and there may be less fullness of the upper pole when you are not wearing a bra.
Two other things to consider. For most women, the recovery will be a little quicker when the implants are on top of the muscle. And, there will be no distortion of the shape the breast on contraction of the chest musculature if the implants are on top. With submuscular implants, there can be a bit of change in the shape of the breast upon actively contracting the pectoralis muscle. This goes away wheh the muscle is relaxed. Usually this is mild and not a problem. However, there are few women in whom this distortion is pronounced and troublesome. Such distortion will not happen when the implants are on top of the muscle.
Hopefully these considerations will help you in your decision making. However, you will have to decide what makes the most sense for you. My best advice is to make sure you are talking to board cerified plastic surgeons (ASPS members) and ask them specific questions about why they favor one approach over the other. You may need to visit them both again. Ultimately you are best off going for the surgeon with whom you commumicate best, and in whom you have the most confidence.