You will want to choose what everyone around you is also choosing. Take a look at the choices made by your peers who submitted their theses before you.

As for the actual question: There is a difference between the concept of "Copyright" and "License". For example, you can put your works into the "public domain", in which case as the author you continue to have the copyright in your work, but you are not retaining any of the rights associated with it; the "license" is how you specify how others can use the work that you have the copyright for.

You will want to choose what everyone around you is also choosing. Take a look at the choices made by your peers who submitted their theses before you.

As for the actual question: There is a difference between the concept of "Copyright" and "License". For example, you can release your works under a "liberal" license that allows others to use them more or less as they see fit; in this case as the author you continue to have the copyright in your work, but you are not retaining any of the rights associated with it. The "license" is how you specify how others can use the work that you have the copyright for.