Based off data from my Polar 720i HRM, I've found that I burn more calories when out on a geared ride than when I'm on my fixed. I think this is due to the fact that my fixed-gear is at 72 gear/inches, which is necessary for hilly terrain like Cincinnati, but too easily lets me spin out and "cruise" when I'm on the flats. When I'm on a ride on my geared bike, I'm able to put a much harder effort in, as I'm able to avoid spinning out.

But, considering that I ride up hills and steep grades constantly, with average total climbing at around 2500 feet per ride, I put the hurt on "better" and am usually as tired as I would have been on a geared ride of an equal distance.

Your mileage may vary.