Self-existence because whatever is the cause of the universe must ultimately be uncaused. If it is not, then the argument just moves back one step. There has to be a first uncaused cause.
This cause cannot exist in the time/space/material universe because then it would exist within the very universe it created. That is impossible.
The cause must be incredibly powerful to have created the entire universe and all of its physical laws.

The cause must be personal because an impersonal force would be deterministic and mechanistic, not possessing free will. A mechanistic being only operates according to the programming it received from something else. But if the cause of the universe received programming from something else, then we have again not provided the answer to the cause of the universe. We have just found a middle-man. The cause had to make a choice to create and only beings who are personal can make choices.

http://www.carm.org/failure-atheism-account-existence

Whatever caused the universe, existed before the universe. Since the universe had a beginning in time, and since matter and energy do not spontaneously change and arrange themselves into something new, then the best explanation for the cause of the universe is an action that was a decision.In other words, a decision to act at a specific time in the past is the best explanation of the existence of the universe. Of course, we Christians would say this decision was made by a personal being who we call God.