The walk is probably smarter for me. But after not running for my whole life, because I didn't think I could and I was scared to try, I've had such a great experience with my bootcamp instructors that the running day, while hardest for me, is my favorite.
One day we were doing a long run and we got to a park and our instructors told us to do "Indian runs" around the park -- groups of five people running at a relatively slow pace; the last one in line sprints to the front and yells HOOAH and then the new last person in line starts to sprint, etc. I backed off and said to the instructor, It wouldn't be fair to the other people in the group to put me in one of these, let me just run around at my own slow pace. Well, he wouldn't hear of it. And the group cheered me on and I made it without feeling like I was slowing anyone down! And I felt so powerful (and kinda young -- which is cool because I think I'm ten years older than then next oldest person). Everything we do is impossible so every day is a victory, but for some reason the running thing really boosts my spirits.
Man, I am so glad to be back with that group.