Childhood...... hands down!
My primary reason for choosing childhood over adulthood is that as child my learning abilities were much higher. Children tend to learn much faster and adapt to their mental environments much quicker than adults do.
Brain of a child is much more agile than an adults as it functions without preconceptions and treat things on it merits rather than pre - fed notions of the society. I would love to have that ability again. The fact is that we think that we are free to think as adults but the sad reality is that an adult human brain can rarely think without a point reference to support to support it. As a child, you need to fist find that point of reference.