I have read The Aquariums of Pyongyang and Escape from Camp 14, both of which are very good. I think that Aquariums is a better overall book, as the author adds context and background throughout the narrative. Camp 14 is more straightforward and limited to his experience, which for a North Korean is quite limited. They are pretty dated at this point (2000 and 2012, respectively) so there are probably more timely options available now.