This is a cop out, maybe, but the answer is: it depends.
Childhood can be amazing... but it can also be crushing. If you're in the wrong circumstances, with the wrong family, there's really nowhere to turn. You just have to wait and hope you survive (both physically and mentally/emotionally). In adulthood, if you're in the wrong circumstances you can work to change them (no matter how difficult that might be). At the same time, you accept the burden of responsibility for your own situation, and perhaps that for your family, too -- not just financially and legally, but spiritually, too. A kid can confidently blame his parents or his teachers or whatever, for his setbacks, but an adult blames himself (deep down inside, at the very least, and whether fair or not). And that blame is heavy to bear.
What I enjoyed most about childhood, in retrospect, and wish I could get back, was the innocence. I didn't understand just how awful things and people could be, and the genuine sense of optimism that was a core part of my character both kept me enthusiastic and hopeful. Now, fairly deep into adulthood, I've seen too much of how mean people can be, how careless, how petty, how intolerant, how vicious.... I bet some other people are motivated by the same sort of things, motivated to fight against them, but I just don't like fighting, and it drains me. Leaves me hollow.
Still, I can't say that I preferred childhood. Childhood utterly lacks perspective; you don't know what you have in childhood until it is mostly lost, and as a child I spent too much time focused on what I lacked, rather than appreciative for what I had, like seemingly everyone else. At least as an adult, I can try to recreate the things I valued as a child with understanding and appreciation of them, rather than taking them for granted. Even if only somewhat successfully. And as a parent, I can try to give those things to my own child, even though I know she will neither understand nor appreciate them until it is basically too late to really enjoy them. It's the circle of life or something.