Originally Posted by Omaha
Weight training is actually more effective for losing weight. Old school thinking says running burns more calories, but that's not the end of the story. Lifting weights may burn fewer calories while you're in the gym, but it will cause you to burn more calories while you recover for up to 3 days.
While I agree with all of this I think you see results quicker from running, provided you run more than 1/4 mile at a time. Back when I was really into things I dropped my weight the fasted when I went to running after a workout. So, to each their own, I prefer a combo of cardio and strength training myself.
I will say, and I said this earlier, if you don't lift weights while doing a ton of cardio you most likely will burn muscle as well as fat unless you are just cramming tons of protein.