Yoga vs. Tai Chi vs. Pilates vs. ?

I have just recent been diagnosed with severe degenerative joint disease of my right hip. i am a young person and my physician thinks it may be hereditary caused. Anyway, I am looking into what form of exercise routine to start using. I do not have access to a gym or instruction, so i will be using a video. I have not tried any of the above three types of exercises. I need something no impact to work on joint care and flexibility. Any suggestions would be appreciated. What video to use. What i should i try.

Start with Yoga, it is simple and easy to follow, then try Tai Chi. I would save Pilates for last, it is the most rigorous.

i think all of them are good
Long term and consistent cardio workout. Stepper, ellipticals, cycling are great ways to raise your heart rate.
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