If you were me, which twitter name would you pick?

Most users on twitter use their first AND last name together. For example, JohnSmith. If their name is taken some users use their last initial with their first name like John_S. Others I have found use their first name, and middle name, followed by their last initial. Like JohnGregoryS. I have grown to like the 3rd one a lot for some reason, but still don't know what to do. I'm 16 years old, and feel like I shouldn't release a lot of information on the net. Luckily for me, all types of these names are available for me to have. My full name (first and last name) comes out to be 12 letters without spaces or underscores. Is that a lot? Currently I'm using my first and last name but I'm thinking I should change it. What's your opinion? Sorry for this longgg question.