Here's a sticky thread on this subject:
http://www.3fatchicks.com/forum/exer...-accurate.html
I personally wouldn't use either method. I wouldn't try to figure out how many calories you've burned. The only way it's possibly useful is if you are figuring out how many extra calories you can eat for the day, though almost everyone overestimates how many calories they burned and ends up eating back more than they actually burned.
Instead, just consider those mysteries calories some unknown number you can bank towards your weight loss. If you are more hungry on days you exercise, maybe add 100 more calories of high-nutrient, protein-dense food (cheese, Greek yogurt, fish, etc). I wouldn't try to eat back any more than that unless you are doing an intensive exercise (swimming/biking/running/kickboxing) 1+ hour a day.