You have to decide what is important to you and what risk you are willing to assume. The reason why there are different opinions and techniques is that there are different advantages and disadvantages. Both can give acceptable results depending on what you want.
Rolls Royces are no better or worse than Ferraris. If you want a fast car, get a Ferrari. If you want comfort, get a Rolls. But personally, I drive a Mercedes and Honda. You get the picture.
Under the muscle technique is used mainly because it reduces the risk and incidence of capsular contracture or hardening, unfortunately, not to zero, though.
Theoretically, over the muscle technique is the most natural because that is where the breast normal lives. Nothing lives under the muscle except for the ribs! However, depending on the size and dimension of your implant, an under muscle implant can look very natural while an over the muscle implant can look very unnatural.
In the end, it is a combination of multiple factors that are interrelated, but not directly comparable, that you need to assess. There is no such thing as best, only choices. Your surgeons should discuss all factors with you. Having all the facts and option, you cannot make a bad choice. You will make the best choice at the time you make it.
Usually, the thinner you are, the smaller the implant you can tolerate above the muscle and the more the under muscle technique makes sense as the size of the implant increases. Of course,there comes a point when the size of the implant will make either technique more unnatural and riskier.