Running

Gentle downhill with some steep uphill sections would be more fun, and running is better if it's fun.

I would prefer the gentle downhill for sure. I tend to think about it in terms of potential energy. Everytime I ascend I store some energy in the form of potential energy. If I descend gently, I can make use of that energy little by little. Every step feels lighter on the way down. If I have to take a steep descend I have to waist the stored energy. If I would use it, I would become too fast and hurt myself. I have to make sure I safely disperse the energy.

I do not have any preference for a steep vs a gentle climb, though. I have to put in the energy either way

I would try to alternate the direction if I find myself developing a preference for either one. I guess it's kind of an introspective approach, but if I start to get too comfortable I always switch it up to avoid stagnation. Forcing myself to run something I don't prefer AND forcing myself to appreciate it challenges me. I like that. I'm Buddhist though, and part of that is the journey of self-challenge and analysis that we undertake.

For me it really depends what I'm trying to feel/do that day. I have a couple routes like that, that I do in both directions. They both have different purposes to me.