Swimming is a shitty form of cardio, coming from someone that did 10 miles in the pool every morning, for four years, followed by an 8 mile run.
Walking or a brisk jog is the best form
followed by Treadmill, as all three are easy on the joints and allow for long term results.
Biking is not only monotonous but both kills sperm as well as causes related long term penile issues, not that you jacked douche bags ever cared about your dicks
lol
For fat loss, there's something about walking 5,6,7 miles a day, that nothing else compares to.
It's very strange.