Claymoore wrote: » If you're trying to collect the whole Exchange set, then obviously you want to do them both. If you only want one to validate your experience, choose 2010. The 2007 exams were a mixed bag. 636 was half Exchange, half PowerShell and was a picky, challenging exam. 637 was incredibly easy and they finally got it right with 638 which was one of the best MS exams I have taken. I took the 662 and didn't think it was too challenging. It was more of an Exchange exam and less of a PowerShell exam. I haven't taken the 663 yet.