What is the most efficient cardio workout for losing bodyfat?

Running, of course. My city is surrounded by mountains, so I try to go walking and running in the mountain parks near my home, or if it's special, far from home. Riding bike is another efficient solution if you don't like mountains.

HIIT is the best at building muscles and losing weight while giving the same benefits as cardio in less time. Increase in muscle mass will help more in weight loss than cardio alone.

You can go for insanity programs ! They are known to be super intense but exist in several formats (20 minutes, 30 minutes, and 1 hour) and don't require any material, only body weight. I'm doing the insanity max30, the 30 minutes one, and it's great !

Hey,
My response doesn't answer which cardio workout is more efficient but rather focus on my personal observations on the topic,"Lose Bodyfat".

I've started my journey to weight loss recently, and started doing my research on the most efficient way to lose body fat. (Including but not limited to Cardio)

In my analysis, it's 80% Diet and 20% exercise, more importantly, one has to be consistent. And view it as a lifestyle shift to lead and much active Life.
Well there another crucial component which in my opinion will make a world of difference is

MINDSET & Knowledge

But my observations are from an amateur's perspective so please I suggest you do your research too.