What a great question!
Of course it is easy from the perspective of having not only been born, but having lived and come to love life, other people, etc to immediately declare that we are delighted to be here.
What is more thought-provoking, though is to try to approach the question from a different point of view - aside from those personal considerations, how do we feel about it on a purely hypothetical level?
That's where it can get harder to answer. Obviously, if we happen to have single-handedly cured hunger, war, disease or something, we might feel like it would be a bit selfish to say, well, no, I wish humans still had all those things, and I had never had to bother with things like root canals or getting up in the morning, especially in winter when it's cold out and I have a cold.
But for most of us, what are the real advantages? How exactly is the world a better place because we are in it? And remember, we are talking about aside from those personal aspects like oh I never would have known my spouse, had my wonderful children, etc etc.
Although, for many of us, it is not easy to remove ourselves from that, although that too can be complicated. Some of us might reflect on what our mothers' lives might have been, had we not been born, and if we are honest, no matter how much she might insist that we are the most marvelous thing that ever happened to her, might she, depending on her circumstances, perhaps have felt that completing her education, maybe achieving a youthful career dream, might have been pretty marvelous, too?
And, as others have pointed out, how, or whether, we even feel comfortable thinking about the subject may be influenced by our cultural/faith traditions, whether the situation of the world today is something we feel good about - over half the world's children, for instance, don't have a childhood. Some people think that's as it should be, and others might not share that enthusiasm.
Of course, just because we might not feel that we can claim that our very existence has made the world an inherently better place, by the same token, it would be hard for most of us to make a creditable argument that our species would have achieved a significantly larger measure of evolution had we NOT been born! I mean, most of us are not politicians. Or even lawyers.
So probably the most reasonable answer is that when you look at the big picture, and consider, as previous posters have reminded us, that it is not exactly like we went through some sort of application process, with interviews and essay questions, as intriguing an exercise as it is to contemplate the issue, in the cosmic sense, our opinion on the subject matters less than our existence!
I was sure if anyone got it, it would be you!