You may want to consider interval training for your purpose. Studies are beginning to show that interval training is better at burning fat than long slow distance (LSD) training, and more importantly, interval training is less catabolic to existing muscle mass than LSD training is. To top it off, interval training protocols such as the “Tabata Protocol” take less than 10 minutes to complete compared to the traditional 30-60 minutes of LSD recommended for fat loss. There is only one potential downside to interval training – it’s HARD compared to slower and longer bouts of cardio.
I personally still like going out for a longer run or putting some mileage on my C2 rower, but I do it for fun, not necessarily for function.
Look at the “Fat Loss” section of this article for more detail:
Don’t just rely on my word or this one article – there is a great deal of research on the internet regarding interval training. A quick Google search of “interval training” or “tabata protocol” will return a ton of good information.