Firstly, congratulations! I cannot think of a life milestone more worthy of celebration than matriculating from a phd program.
I like both the pieces on your shortlist. I'm sure either would bring you great pleasure. However, if forced to make a decision, having tried both on, and having regard to the context in which you intend to wear the watch, my suggestion would be the Blancpain. The Breguet has quite a unique 'baroque sport' aesthetic and the bold lugs make it wear larger than its nominal dimensions. It will therefore stand out more - nothing wrong with that, but perhaps not what you are after given that you don't want to attract too much attention. Also, as a mathematician, the Blancpain is the more technically interesting piece, with well integrated and useful complications in the alarm and dual time. One final thing that would personally drive me crazy about the Marine - the seconds do not hack. For idiosyncratic reasons, I can deal with that in a sub-seconds, but not in a center seconds.
Best of luck in your watch shopping!
Kind regards,
MG