Swimming in my opinion, is one of the best exercises, is a great way to get fit, to be healthy and you could practise it in differente styles and places, but there are other things to consider to stablished if it is the best exercise.
For one thing the advantages of swimming, doing this, you put in motion all your body, bones, muscles, etc., but also your lungs and heart, so it tis a complete exercise and you don't need to be a professional to enjoy it an have the benefitis, yoou need to be constant and after a while mixed with other types of excercises.
On the other han if you don't know how to swim or you don't have a public pool or the se near you, could be a little expensive starting to swim, because you have to pay for the equipmente, the lessons and after that for using a swimming pool. And also is not a free-risk exercise, you could slip and fall, broke a bone or get an eye infection.
As a conclusion I think is a good exercise you just need to take into account that as every other exercise it has its risks and needs discipline to get better a it.