I weigh 120 and would love to have ass SHOTS or implants. Which is better?

Your options about buttock augmentation should be discussed with a plastic surgeon after detailed evaluation. Providing that you have sufficient amount of fat to be harvested and used as augmentation "material" my suggestion would be fat grafting. It seems that implants available in USA and FDA approved have significantly higher complications then fat grafts. They should be used only for selected patients and by  surgeons with significant expertise in buttock implantsI suggest you to start with a consultation with a plastic surgeon with expertise in buttock augmentation. Good luck.

Being that you are only 120 pounds you may not have too much fat for us to transfer, so implants may be better to give you the results your looking for. Best of luck.