As genuine as your question is, there are no good answers. The way we ended up with a Big Four is that the Fifth member of the Big Five (Arthur Andersen) audited Enron, essentially telling everybody that it wasn't an enormous fraud, but it was. All the senior people at AA avoided jail but the audit firm was so obviously untrustworthy it folded. But that doesn't mean the other Four are fine, it just means the "Too Big To Fail" problem is far worse for audit firms than for banking. If we took down one of the Big Four it would probably tank the whole world economy, and they know that, which is Not Good.