I know Leo has decided to do Judo (at the time of writing) but I would like to add something else that popped in to my head the other day.
I think overall Judo is a better cardio workout. My reasons (which are based only on my own observation) is that in Judo randori, you have to be explosive and work hard for the entire time. In BJJ (particularly with a Gi), you can stall a lot easier. The better you get at BJJ, the less energy you use too.
Someone on another forum once asked how many calories would a person burn in an hour of BJJ. One poster summed it up nicely:
"When you are a white belt, you'll burn about 800 calories in an hour. When you are a purple belt, you'll burn about 300 calories in an hour!".
These of course aren't accurate figures, but it was a fair point. BJJ at a higher level doesn't require the same amount of constant, explosive movement Judo does. Yes there can be explosive BJJ matches and I'm not suggesting BJJ isn't a tough workout or you don't sweat, it's just BJJ at more advanced levels is more about conserving energy . This might make you a more effective fighter, but it might also mean you don't tax your body the way a Judo workout will. Even at an advance level Judo players still have to constantly work hard, and there is less scope for stalling.
"Let your food be your medicine, and your medicine be your food"