I'm a fan of both franchises, but I would recommend Potter. Just a few months ago, I watched the entire series over a 10 day period and it was a lot of fun. I sometimes forget how little the kids were when this started! Seeing them grow up made me feel a little sentimental. I also loved being reminded of so many things that I had forgotten took place. Anyway, I would say you can't go wrong with Lord or Harry as a re-watch marathon, but my recent experience leads me to nudge you in the direction of Hogwarts.
Enjoy your 3 days!!