I've been married twice, and lived with someone (committed, monogamous) two other times. I have a toddler (young child at this point? What is 3 and a half?) and an infant. I don't particularly believe in marriage; I treat couples without children in the house as essentially single people. I often _refer_ to unmarried parents with kids in the house as married and married folk without children in the house (even if grown) as single, and I'm just waiting for the day it gets me in to trouble. I don't think that means I think parenting is harder than marriage or vice versa. I think it means that the parenting relationship while the kids are at home takes up a lot of time. Way, way more time than marriage does, even if you work at the marriage. Possibly this will not seem as true to me when the kids are teenagers, but parents of teenagers tell me they are more demanding than infants so we'll see.
I will say one thing. Being a child being raised by my parents made me want to die. Being married to my first husband made me want to kill him. One of the live-together relationships made me want to die. That has not happened with R. Or with A.
But some nights with T. I definitely got extremely tempted to engage in violence against someone, identity subject to change from second to second -- all of which could be directly attributed to sleep deprivation.
I don't much care for generalizations about the kids -- girls are like this, boys are like that, first kids are one way, second kids another (altho I do like the third-kid-will-surprise-you theory). I think I don't like this question for the same reason. It isn't whether marriage is hard -- it's about whether _a_ marriage is hard. It isn't about parenting being hard. It's about whether parenting a particular person is hard.