As others have said, just depends on what you enjoy. The most effective weight loss exercise is the one you can do everyday and with the most intensity. Personally I like swimming and sprints. Sprints seem to be my 'go to' cardio workout as I thoroughly enjoy doing them and they seem to be much more muscle sparing then jogging, plus they don't seem to be so hard on my joints. I swim in the winter when it's rainy outside.