Running promotes the best overall physical fitness in my opinion. It engages all of the major muscle groups, improves cardiovascular health, and burns a significant amount of calories. Plus, it's accessible to anyone - all you need is a good pair of shoes and some open road or a treadmill.
I believe that swimming promotes the best overall physical fitness because it works out all of the major muscle groups in the body, helps improve cardiovascular health, and is low-impact on the joints. Additionally, swimming can help increase flexibility and endurance, making it a great full-body workout.