What is the best and safest== injected breast or silicone breast?

Fat Graft. By injected, do you mean a fat graft. This is safer as it is your own tissue. However, the size that you will end up with is a little more unpredictable as it will depend on the harvest from another site and also how much will take onto the breasts.
Other than fat, There are no fda approved injectable fillers designed for the breast. So, it's either autologous fat grafting, or a breast implant.