If by "best", you mean the most fun, then it is swimming... at least for me it is.
If you more clearly define your goals or what you like, you'll find what your "best" cardio is.
I know that for swimming, how "good" it is depends on technique. For poor swimmers, swimming often does little, but for excellent swimmers it is a total body workout.
"The worker has the right to leave his boss, but can she do it? And if she does quit him, is it in order to lead a free life; where she will have no master but herself? No, she leaves to sell herself to another employer. She's driven by the same hunger. Thus the worker's liberty is only a theoretical freedom, lacking any means of realization; an utter falsehood."