This will mainly depend on what you enjoy. If we are strictly talking about calories burned from running vs swimming, running burns a bit more calories than swimming.
A 150 pound man running at 5-6 miles per hour, which is a normal running speed burns about 300 calories per 30 minutes.
Swimming on the other hand, with a freestyle swimming burns a little more than 200 calories per minutes.
This is just a rough estimate, but factors vary based on intensity and how consistent you are with your exercise.
Which Is Ultimately Better?
At the end of the day, it comes down to what you enjoy. If you enjoy swimming more, you more than likely will spend more time in the pool and thus burn more calories.
Swimming is easier on the body as well, since you don’t have any impact on your joints and knees like running. You might actually improve your posture and get a little a bit taller…