It doesn't have to be the most practical or common distance. Just whichever one you enjoy the most in the moment. For example I currently run 5 km a lot at the moment due to lower levels of strength in my calves and the practicality of it (5 km doesn't take much time out of the day), but I definitely enjoy 10 - 12 km runs a lot more and would like to build up to them again. They give me more time to enjoy the sensation of endurance running and I like the harder mental challenge of maintaining a consistent pace over a longer period.
It’s long enough to be worth going. It’s enough distance to hold a warm-up, cool down, and whatever kind of tempo, fartleks, hills, or whatnot you’d like to toss in the middle. If you’re just taking it easy around town you can see some stuff. And I get done before I get bored.
For regular running, 12k. I wouldn't mind anywhere between 10 and 12k, it just so happens thar I have several regular routes that are around 12k. For racing, half-marathon. Long enough to strategise, but short enough where at my level I don't need any special considerations regarding nutrition and fuelling.
I enjoy running on my lunch break at work, so a shorter run is good for me. I'll run 2 miles most days but every few runs I'll run 5km, just to see if I'm improving.
My average mile time for a 5k. Is like 9 minutes a mile right now, so I'm not an advanced runner by any means.
For racing, half's are my favorite, despite not racing them often. Long enough to be hard, long enough to not be a pain cave race, but don't destroy you for weeks to recover.
For a day to day run, 8 miles/12km is a good sweet spot for me. A good duration, but not too long, not much recovery needed. Can just go do it.
I am pretty overweight. I can run up to about 10km, and my heart/breathing is fine, it's just my legs that start to give up. I've gone for three runs in the last 8 days, longest being 4.7km which I was pretty sore after. The other two were 3.7 and 3.8. I felt much better after those.
I like 8-10k. Far enough to get me in the right frame of mind and quick enough to fit in most days I need to.
I do enjoy 20k on a Sunday morning plenty of time to catch up on a couple of podcasts.
7-10k seems to be my sweetspot at the moment. I can manage all my run-types in less than 60min. makes it a lot easier to fit in my daily routine => less planning and stress to fit things in => increased enjoyment
Probably the 10k. It's a nice round number and also the first distance I ran in a race (except for races as a kid). I think it's also the distance that suits me the best.
My normal runs are around the 8k mark but I really enjoy when I go on my slightly longer 10k runs. I would love try a half-marathon at some point in the near future if I can build my endurance enough.