In my opinion, these two are very popular these days. Running is very accessible to almost everyone and is really a very good cardio exercise. Biking on the other hand is also a very good cardio exercise but needs more investments. Despite that fact, many people are into it. Is it because they are reducing their carbon foot print as their way of helping save Mother Earth thus biking instead of bringing a car? I do not know but I like the idea.
I say they are popular because when out on the road, I always see cars whith thule bike racks holding one or more bicycles at times. Online, I often see news about a new upcoming fun run almost everyday.
My hubby is into both but for leisure and health purposes only. I? Maybe I would do running but not biking.