I'd stay from running. Just too hard on your joints, especially if you're carrying a bunch of muscle. When running, you'll land with a force of about 2.5x's your bodyweight with every step.
Do the elipticals or walk on a tmill. Longer distances will build endurance better than high intensity bouts.
In the end, it comes down to why you're doing the cardio, i.e., to burn fat, health reasons, wanting to do a marathon, or as you mentiond, to improve endurance.
One last thing, if you're doing a treadmill or walking outside, wear good shoes. Running shoes will absorb the most impact forces and save your knees when you're an old man!
As Kurt Vonnegut once said, "Take care of your knees, you'll miss them when they're gone".