Reports by Posting Date vs. Document Date

We are having a discussion in our company as to the preferable (correct) format for printing our financial reports. I feel that Posting Date gives us a clearer picture and is the default I have used to reconcile to our CPA. However, my supervisor is asking me to prove that theory. I can find no documentation in SAP help that gives it in black and white. I would like to have input from someone who has used the program for a time and has an actual guidelines for which is correct.