"which one is [more] appropriate?"
As I said before, the answer to that question depends on how you expect students and teachers to use your activity. I don't know enough about the activity to be able to judge.
As I explained before, the reason to choose one or the other is the question "Do you want your activity to be part of Moodle quizzes, with other question?" If yes, do a question tpe. If no, do an activity module.
There is another reason to choose one or the other. Making an activity module is easier to start with. You can just copy http://docs.moodle.org/dev/NEWMODULE_Documentation, and very quickly get to the "Hello world" milestone. Activity modules are quite independent, so you don't have to understand many other parts of Moodle to create one. In comparison, creating a qusetion type is quite hard until you learn a lot.
So, my guess is that you should create an activity module.