It depends. If the main problem is a loss of breast volume, without too much sagging of the skin, a breast augmentation may be sufficient. It has the advantage of being a simpler procedure with a smaller scar. Breast implants by themselves can sometimes improve mild degrees of droopiness.
However, if there is significant sagging/drooping, then a breast lift (mastopexy) may be required to correct this. This procedure can also be done together with an implant (a mastopexy augmentation) if an increase in volume is also needed together with a correction of droopiness.