Charlotte or Jillian

You can't spot-reduce fat, so if you're working a specific area of the body, you're more likely building/strengthening muscles *under* the fat. You must eat less than you burn to lose fat (and some kind of strength training is a good idea, to maintain as much muscle as possible). I love some of Jillian's workouts because she hits everything and raises your heart rate, but I haven't tried Charlotte, so I can't really speak to that.
Do what *you* love, because that's what you'll stick with. But do try to find something that works your whole body so you're not creating imbalances and other problems. Good luck!