Is it better to go for depth or breadth in your studies?

Jobs seem to be getting more and more specialized, especially jobs that require a high level of education. If you have a lot of different interests, would you rather follow up on all of them? Do you think you can reach your maximum potential if you do this, or if you concentrate on reaching an expert level in just one subject? If you have chosen to go one way or the other, are you happy with the choice you made?