The philosopher Peter Singer writes that Christians have failed to come up with a satisfying answer as to why God allows suffering (here). I think most Christians base the fact that there is suffering on the effects of sin stemming from the original sin. Singer believes the original sin was about wanting knowledge. I believe it was about pride. Singer debated with Dinesh D’Souza at Biola University. The points that Singer says D’Souza made were neither satisfying for me either.
Watch the debate here.
TK also thought D’Souza’s argument was weak (here).
I thought Philip Yancey did a good job of discussing the problem of pain in his book.