Which is harder sub 1 hour 10mile or sub 3 marathon?

Maybe, but a lot of us including me chose to answer the question as we sit with our known strengths and proclivities without regard to 'with proper training'.

After nearly 40 years of running, I never have and will never have desire to do "proper training" for a marathon. I also have no desire to rot out more of my teeth eating gel/sugary drinks on the regular to do proper training and racing. Therefore if I'm doing a hard long workout, I usually bonk after about 1 hour in training, maybe 1.5-1.6 hours in racing with more attention to being fully fueled than before a regular training run.

For me, it was always easier to run sub 1:00 for 10 miles, than sub 3h for the marathon. I have done both many times, ultimately running sub 49min, and sub 2:18.

Started properly training for running at 16, went through DI, competed nationally, but I could quite easily run sub 1h for 10miles after maybe 2 months of regular non-soccer jogging (i.e. typical HS short intervals and 20-30mpw). During HS, I ran several road 10milers during summers, best being 53min as a junior. Sub 1h was a regular midweek steady state run since junior xc season.

Ran my 1st marathon as a bet during college as sophmore - I had claimed during argument with much more mature runner that I can beat his PR without any specialized marathon training. He was 2:24 marathoner in his 30s. Boy, was I wrong. Went through 1/2 in 1:10, finished in 2:59:57, barely walking. Got pat on the back for fighting spirit 😀. One of my hardest runs. My 10000m PR at that time was 29:20.

Eventually got it, and could run sub 3h in any long run not involving very steep and long climbs, but it was never easy. Never. Even as a high mileage runner. Sub 1h for 10 was an evening run on any day of the week.

Even in my late 40s I can still run sub 1h for 10M (in a race, not on a training run). I would not attempt to run a marathon. In my mind, marathon is a hard race, and I am long done with hard racing... I might be able to run sub 3h (or not), but I don't care to find out.

59:29 (track) and 2:50:20 (blew up) , both at 18-19, in 1962.

When you are that much faster than the performances in question, you’re basically just saying you found it easier to run for 1 hour than to run for 3 hours, as the ability to cover the distance in that amount of time was never in question for either. Sort of like me saying it’s easier for me to run 10 miles in 2 hours than to run a marathon in 6 hours.

The 10. In the last 10-mile race I entered (about 15 years ago), I ran 59:59, and decided that was a good last “serious” effort for me. I was never very fast - gutting out that string of 5:55-6:05 miles and then kicking it in just before the clock struck 1:00:00 was a real thrill for me. Running 6:50’s for 3 hours on end and hoping I don’t die was not similarly thrilling. (FWIW my PRs are from around the turn of the century and are faster than the times in question but not by a lot. Both of those would be well within the range of disappointing but not terrible days for me at my peak before I got old and fat.)

Isn't it the same for just any random distance and time? As I have tried both many times, I chimed in with my experience. There is no doubt that sub 1h 10M would earn you more points in just about any chart than sub3 marathon. The whole discussion is about personal experience. I find running for 3 hours at sub 7 pace harder than running 1h at sub 6 pace. That's all.

I'd say it's quite easy to run a mile in sub 1 hour 10...