I try to always reply honestly when talking about having kids. And I'm lucky to only have friends who do the same.
Usually I say something like "It's really hard, but it's so awesome at the same time that you forget how hard it is all the time. In the end, you feel like it's worth it."
I confess I wasn't that positive when I was totally sleep deprived. I also have the impression that no two situations are the same... Some parents have it very tough while some others have quite an easy time with their kids. You gotta have some luck...