I don't think that there is any one best or worst cardio exercise for you or anyone else. The key thing is to find an activity that you enjoy enough to do every day. The fact that you like something enough to do it several times a week means more than any other feature of the activity itself.
I would begin with walking. No matter how bad your lung disease might be, you have to get around, and taking nice slow walks for about a half hour at a time is something that you can and should do every day -- or more!
If you can do that, then many experts would recommend picking up the pace so that you are walking at brisk pace, like 4 miles per hour. If you can do this, then you might consider some other activities, such as bicycling or swimming or just wading in a pool.
My main advice is to get out there and do something. Don't get paralyzed searching for the perfect activity. They are all good!
