I'm talking to myself. When I'm alone, I do it out loud. When I'm in public, I do it silently. That's my natural way of thinking. When I speak or write, I have the internal dialog that matches what I say. Some people say that I'm good at writing and I attribute this skill to the habit of "playing with words" in my head.
However what I talk about internally is the images that rush through my head. I'm thinking in movies and just comment the most important bits out of these movies. I think that this habit formed in my early childhood, when I would read a book, see it in my mind and then remember is and talk it through as if I am a character in a book.
Nowadays I have a good control of my mental processes, I can switch from visual thinking to sound thinking to internal dialogue, to sensual thinking and mix and match them all as I need. Each way of thinking is useful for different things.
And of course I can switch the voice in my head when I need to (meditation, visual experience, sex etc). Comes with practice.