It depends on your goals. Practicums allow you to try out different kinds of jobs. If you're not sure what you want to do, two practicums in different fields make sense. If your goals are clear, an internship will allow you to concentrate your efforts. Practicums also make more sense if you're trying to graduate on schedule.
Internships require an extra semester.
The prerequisites are senior or graduate standing, completion of 15 hours of broadcasting courses, gpa of 3.0, and consent of department head. Usually internships are taken in the summer before or after the senior year. By then you will have had enough courses to be able to take full advantage of the internship opportunity. Also, you will be near enough to graduation to use your internship as a springboard to get a permanent job. The department is reluctant to allow anyone representing us to show up at an internship without a solid knowledge of the field.