Cardio is typically boring, so even if the cardio workout burns a lot of calories, it doesn't mean someone will actually do it for long. Instead of trying to figure out the most effective cardio, think about what cardio you will actually do for more than a week.
For me, the only cardio that doesn't leave me completely bored is: hiking, martial arts, and Zumba. Yeah, I do Zumba only because it doesn't bore the crap out of me, not because I think it's super effective.
Of course, there are also some sports that are pretty high intensity such as basketball, tennis, and squash. But I don't see many buff tennis and squash players.
But, then, it comes back to your goals. Why are you working out in the first place?
For example, I love hiking, so my workouts are around how I can make my hikes as enjoyable as possible. I don't want to finish a hike out of breath. I want to enjoy the scenery and explore. Likewise, I don't want to be huffing and puffing half way through a martial arts class either, nor do I want to pull any muscles, so I have stretching goals as well.
I hope this helps.