Without any doubts each university is the whole different story. All have their own history, policy and program but, anyway, most of them require such type of work as dissertation writing, in most cases you have to do that each year. The best suggestion in topic choosing for you is to use brain and think logically. You should choose the subject you are interested in. It is very good when you are writing dissertations on the same subject every year, just change the topics every time getting more difficult, so that finally your senior year you will have enough material for the diploma and will have the brilliant defense on it.