I've run two marathons and I have two kids. I can't compare the two. If you choose to get pregnant you have no choice but to give birth but training for and completing a marathon is a choice you can change at any time.

I had really great birth experiences and both my marathons were successful. Both were welcome challenges!

I have done both.  I have given birth twice and the second time was a piece of cake.  My first and only marathon was pretty difficult.  I had trained hard and was nursing some nagging injuries.  I remember at around mile 21 thinking that maybe running a marathon was harder than giving birth.  Given that my children are now 11 and 8 maybe I've just forgotten how difficult giving birth was.  All I can say is that while both are very different challenges, they are nonetheless very challenging.

That was going to be my answer too!  I have three kids, and if I could have had an epidural, the marathon would have been just as easy  

However, I'm sure the answer would be quite different from someone who gave birth without any meds.

I have three kids. I'd say giving birth was easier (no meds here). The reason is, you don't have any choice... you can't quit the birth process... the baby's going to come out one way or another. Plus you know you're going to feel great when it's over. With a marathon the mental effort is so much greater. I guess for me, mental strength is "harder" than physical strength.
Unmedicated labor is definitely not the most terrible pain I've experienced. A blow to my knee in a soccer collision was much, much worse.

two marathons and two children for me too.  Birth was much more difficult for me but I didn't get an epidural.  the pain was excrutiating during childbirth, and the pain for the marathon was only moderate.

When my wife and I were in child birthing class, they said the energy expenditure was actually pretty close, with the marathon being slightly more. Pain is another issue and drugs make the question harder to answer.

I've thought about this a lot.

I am a certified childbirth educator. I taught Lamaze for 10 years. (a long time ago)

I used to say, "Labor is like a marathon but you don't get a medal at the end, you get a baby."

also, "Labor is like a marathon except... you can step off the course in a marathon. The only way out of labor is to give birth, either vaginally or abdominally."

SO.

I have been in labor and given birth 3 times.
First two, pitocin and epidurals.
Third one, pitocin and no epidural.

I must say that the best experience was the third one, because recovery was so quick, no epidural, so I was in the shower within an hour after birth. Good recovery.

BUT.

I was a big fat liar about the marathon analogy.

I have started and finished 11 marathons. There is no way I could have "...stepped off the marathon course." I had to endure until I "gave birth"... in other words... crossed the finish line.

My conclusion:

It is unfair to compare labor and birth and marathons.

Here is why I decided that:

I love homemade cheese ravioli and tomato sauce.
AND.
I love blueberry pomegranate smoothies.

Which one is better?  It is impossible to compare the two.