Which has greater Fat/Calorie Burning impact?

Fat burning during exercise is irrelevant.

The first example will burn more calories, mostly because it takes longer. However, that's an overly simplistic way of looking at things. There are more factors to consider.

I don't know about burning calories, but I've always been told that if you're wanting to build muscle you need to do max weight, less reps. For example: if you're doing 4 sets of 20 curls with 30lb (just an example) and then the following week you increase your reps to 25, you're training your muscles to lift the same amount of weight for a longer period of time. You're gaining muscle endurance, but you're not actually training your muscles to lift a heavier weight. I learned that if you're trying to improve your strength, then you need to lift more weight, less times. And when that starts feeling easy increase your weight, not your reps. I by no means am a fitness/training expert! I was just sharing what I've learned. I don't even know if it was relevant to what you're asking!! Haha! But hopefully it helped a little!