I talked to my lawyer extensively about CP vs. I-485:
I was about to take the CP route since it is typically shorter, but I realized that I had no way to get EAD for wife during the process of CP. Also, if it gets denied for whatever reason, you cannot appeal although he said that is very unlikely provide you present all documentations. On CP, you also would need to be available to travel to your home country on a short notice.
That said, I can tell you that if I had filed CP, due to the cut-off dates imposed I guess I would be really frustrated by now. I filed I-485 on Feb 22nd 2004, got EAD for wife (who has been out of the workforce for 5 years now and desperate to go back to work). If I had filed CP instead, if I understand correctly by now I would be unable to get the greencard due to the cut-off dates imposed. Can you imagine that ?
I reckon this is just a matter of circumstances, and in many cases CP turns out to be a very good option.