Both biking and walking have tremendous benefits. Choose the one that you enjoy the most and that is the best exercise — for you.
Here is a good read: https://www.livestrong.com/article/387574-which-is-better-exercise-walking-or-biking/. Also below is a link to a PDF detailing the “Physical Activity Guidelines for Americans 2nd edition” from US DHHS.
Please note
This information is not meant to replace the advice of a physician. You should not rely on any information or suggestions here to replace consultations with qualified health professionals regarding your own specific situation.
Sources:
07312019 walking vs DHHS PDF - https://health.gov/paguidelines/second-edition/pdf/Physical_Activity_Guidelines_2nd_edition.pdf#page=55