Though these certifications can be taken in any order, if I were you, I would first take the SCWCD. Because its more logical to read about web servers and web components first before going on to EJB's. Not only is the SCWCD easier than SCBCD, you'll also learn more as it covers a wider range of topics. You'll learn about enterprise design
patterns, for example which would give you a broad understanding of how J2EE applications are architected. I feel that doing the SCWCD first and then SCBCD is more logical.