I'm getting mixed answers about using treadmills/best choice cardio. what do doctors recommend?

Mixed answers.: Because there is not one answer. If goal is fitness working out 30 minutes 3- 5 times a week. Work out should be balanced upper and lower. If you want to perform well at something you should train for it. So... if you want to run 5-10K then get out and run. If you don't care for that run on a treadmill. Recognize that both forms of running are associated with a variety of injuries.