We generally ask the poster to describe the situation in which you plan to use your sentence -- we call that 'context'. We also would like to know what 'it' is; is it a room or an apple? Which we would prefer depends on information like this.
In general though, "I will share it" describes a one time act in the future, while "I will be sharing it" describes an arrangement that goes on for while. Also "I will be sharing it" would be used as a background for another action.