I’ve heard that the CSW exam is on par or a little harder than the Certified test (theory portion only). The only thing about the CSW is that the test is a little heavier on labeling laws than I felt was necessary. The published study guide from SWE would be good for any wine geek.
CSW is easier than Certified, and definitely easier than Advanced.
CSW is just a memorization exercise of the text they give you, Certified can have questions about anything form anywhere. Pressure of service is hard for everyone, getting questions shot at you while serving Champagne.