Which would you recommend; Mentor vs Sientra? (photos)

Both companies make implants that are FDA approved and can produce good results. Far more important than the subtle difference in the implants that you cited is the artistry, skill, training, and experience of the plastic surgeon who surgeon certified by the American
Board of Plastic Surgery and ideally a member of the American Society for
Aesthetic Plastic Surgery (ASAPS) that you trust and are comfortable with. You
should further discuss your concerns with that surgeon in person and make the decision with him or her.

Robert Singer, MD FACS

La Jolla, California

Thank you for the question and pictures. Based on your photographs, you are starting at a great place and should have a very nice outcome with breast augmentation surgery.   Personally, I think that you should do well with any of the FDA approved breast implants ; much more important will be the recommendations below: 1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.  2.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "C or D cup" etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.   Therefore, I ask that my patients not base their communication preoperatively OR  their satisfaction with the outcome of surgery postoperatively, on achieving a specific cup size. The use of computer imaging may be very helpful during this communication phase.
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery.  The use of temporary intraoperative sizers, viewing the patient's breasts in the upright and supine position, are very helpful during the breast implant selection process.
I hope this, and the attached link, helps.  Best wishes.