This is a very common breast augmentation question but I always remind patients that the difference between the breast implants you are considering is just 30 cc or 2 tablespoons.  The best way to decide on a size is to place trial breast implants under a tight fitting sports bra.  That way you can chose a breast implant size range that suits you.
Make sure you research the subject of breast implants very carefully as there is a lot of information that you should be aware of such as:
·        The implant with the lowest capsule contracture rate.
·        Gummy bear breast implants.
·        Rapid recovery breast augmentation.
·        ALCL and breast implant illness
·        Above or below the muscle pros and cons.
I always recommend that you make sure you see a Board Certified Plastic Surgeon who has access to implant like Sientra breast implants.
Here is another link to information on the best breast implant