Running is harder and will burn more calories. Cycling is also good but it depends on how hard you ride. What ever exercise you chose you want to be working hard enough to get your breathing to the point where you can still talk but not sing. It will take several weeks before you start to see results, it takes time to increase you metabolism and burn a lot more calories. Diet is very important, it's much too easy to out eat any exercise you do to burn off calories.