Hi Iaa,
Thanks for the question! Mentor CPG implants are fantastic because they come in so many shapes and sizes it's pretty easy to customise one that is specific to your body shape and breast type. As a general rule, I tend to make a decision to use a tall implant if the patient is also tall or has a long torso/breast. In terms of which would be more 'natural' there are two important things you should consider. Firstly make sure the implant is placed partially under the muscle in what's commonly known as a 'dual plane approach'. Secondly, make sure you don't choose one that isn't too big!
Whilst we're on that topic, make sure you see a fully qualified plastic surgeon. Ideally, chose one that has a Vectra 3D simulator which can be extremely accurate and give you the peace of mind that you have the right implant prior to going into the operating room.
We've done a series of 'Breast implant essentials' videos to help people make informed decisions in this regard. You can find them here:
 http://www.parkclinicsydney.com/plastic-surgery/breast-enlargement
Hope this helps. If I can help with anything else just call through to the clinic.
Kindest regards,
Alex