I would recommend going to a workout store and seeing what works for you knees. I would also visit an orthopedic to see what your issues are. Therapist can help a lot.
I have patella tracking issues and arthritis, degeneration of cartilage. The elliptical kills my knees. The bike, treadmill on an incline an bikes are the only things I can do. My friend that has bone on bone knees loves the elliptical. I think you have to find out what works for your body.
I have been to three PTherapist over the years and all have recommeded bikes for my knee issues, non weight bearing is preferred. According to my orthopedic. Bike and swimming are great, elliptical if it doesn't hurt, treadmill and walking ok, not at the top of his list, and running a no-no.
Of course if you love something and it does't cause pain you have to weight the risk. I am trying to put of knee replacement.