Hi Yassine,
I don't like rating certifications in terms of difficulty since difficulty is mainly subjective
As certification exams are originally intended for people with a solid experience in the tested domain, one who has worked for a certain amount of time with the technology (EJBs or XML) should not have big problems with the exam
The SCBCD exam aims at
testing every little tiny details about EJBs while the XML exam aims at testing every little tiny details about XML
The two fields have not much in common and are thus not really comparable with one another. I know that what I'm saying is probably helping you that much, but anyway... I have my own personal opinion of certification exam and their value, which might not be suitable to someone else.