Rope jumping is good. I think it's even good for your knees, as I've read on bodybuilding.com
Still, it doesn't make too much sense to me. I'll skip, if I wanna get to sweat quickly. Maybe if I'm 30 minutes away from an appointment, and I can jog, so I quickly skip, and bathe and run out.

But about swimming, about the myth that the water carries your weight, think again.

Now, run 50 meters, at your maximum capability.

Do 1 LAP, 50 meters, freestyle or butterfly at your maximum capability too.

At the end, you'll probabbly be panting your breath out. Does running make you pant harder than swimming? I don't think sooo.....anyway I do run, before training that is. Apart from that, nah, I hate running.