There is not a specific type of cardio exercise or workout that is best for burning fat without losing muscle. The impact of any cardio workout on fat loss results depends on a few different elements. If your calorie intake is very low consistently and you are doing high volumes of moderate to high intensity cardio then this would most likely produce some undesired results.
That said, the best cardio workout to get the desired fat loss results can be any type of cardio exercise that has the right balance between intensity, duration and frequency that works well for you.
All the variables should be adjusted to fit your goals, preferences and circumstances to be able to produce optimal results without going to the extreme. I think that it’s a good idea to use the intensity of an exercise to determine the best duration and frequency.
As you would know, there is a big difference in the amount of calories you’ll burn from walking and the amount you’ll burn from running. Therefore, a smart cardio workout plan would have longer duration and more days of walking than running. This is also more practical as the harder you workout the less time you’ll be able to spend working out since your body is not a machine.
My advice is to choose any cardio exercise that you can handle and set the variables as they fit you best, but also adjust your approach according to your results.
Also, you don’t have to worry about cardio making you lose muscle unless it’s very high in volume and other negative conditions are present such as very low calorie intake, lack of protein and no proper weight training.