During this n=36 study, the optimal fat burning zone - i.e. the point at which one has the highest fat oxidation rate - occurred on average at 54.2% VO2max.
However, the great variance between the participating individuals makes it hard to pinpoint this as the fat burning zone.
Interestingly, this article by Alan Aragon, suggest that while fat burning is seemingly higher during low-intensity cardio, post-workout fat oxidation was higher after high-intensity cardio, and that if one measures the effects of the two after a 24-hour peroid, it evens out.
It also gives some insight into the difference between pre-workout meals, and lack thereof.
It then states the following, which I will quote directly to avoid any errors caused by interpretation:
In long-term studies, both linear high-intensity and HIIT training is superior to lower intensities on the whole for maintaining and/or increasing cardiovascular fitness & lean mass, and are at least as effective, and according to some research, far better at reducing bodyfat
I think these findings only serve to strengthen what we already know about the fitness industry; individuality is too prevalent to really make any foolproof claims about which regimen is best for the goals we aspire to.
Especially, anyone who claims to have a be-all end-all piece of information should rarely, if ever, be taken seriously.
Only you, by trying both/all regimens, can discover what works best for your particular body, which is surprisingly different from everyone else's.
If you want results, you should start by picking the regimen which makes you most excited. Not only does it seem like it will be equally effective as the others, but it might be even more so if you enjoy it, and are able to keep motivation high.
Try one regimen for a few months, and measure your progress as best you can. Then you can try another regimen for the same period, and see how you feel about the execution and the results.
Even if the most enjoyable one isn't the most effective over a short span of time, it will likely keep you motivated for longer, and yield the best long-term results.