I like to do both, stationary bike and run. In the winter time when there is snow on the ground and it is bitter cold outside I usually run on the treadmill. However I get bored on the treadmill so I alternate the stationary bike and the treadmill. I don't think that one is better than the other. The bike is definitely less impact so that is always good for those hurting joints.
I get bored easily while riding the stationary bike. I tend to get distracted and get off the cycle and wander away to do my chores. I never get much of an exercise on it. I prefer walking or jogging to this. It is a mood up lifter to be in the open. To breathe fresh air and to enjoy nature makes jogging or brisk walking more fun. You never feel it is tedious especially if you have buddies who will walk the distance with you. I enjoy walking /jogging or outdoor sports to stationary biking.
I would prefer jogging for the outdoors experience. But I guess a stationary bike would be a great workout tool too. My bike kinda broke down and I guess I didn't have enough time to get it fixed. And there really isn't much of a bicycle lane in our place. Besides, traffic is too heavy that's why I prefer jogging as cardio aside from the occasional swimming routine.
I prefer walking over other exercises. I can't do jogging as it is too high impact for me and always causes strains on my body. I am also not that physically fit for this advanced exercise. Walking, on the other hand, is low impact and something I can do for hours outdoors and indoors. It's the safest exercise for people like me who gets tired easily and has trouble catching breath at times. I love to combine walking with working out on a stationary bike which offers resistance and helps build muscles faster which makes calorie burning more efficient
This would depend on the kind of home and neighborhood you have. We live in a nice village and walking is one of our hobbies. There are lots of trees here which makes walking a bit pleasurable. In fact, I always walk on my way to the market which is half a kilometer away. Being a diabetic, my brother-in-law needed exercise so he bought a treadmill. They live in a neighborhood which is scary to walk, you know what I mean. You can be mugged or even raped. In those cases, using a stationary bike or treadmill is the better option than walking.
There are times when I enjoy the bike more but those are rare and I still prefer to get out and move and see some things. It just adds to the excitement and gives me something to do.