Go to Barcelona. You can be there by noon Friday without a super early wake up (or by lunch ~2pm if you want to sleep in) and stay until ~6 pm Sunday. Barcelona is a can’t miss if you haven’t been. And the train stations in both cities are very centric. If you do 2 day trips from Madrid, you will spend as much time in transit. You wouldn’t have to change hotels, true, but I would do Barcelona. Food, design, atmosphere, architecture, the sea ...