As you may know already, SCWCD focuses on the web tier (
servlets and JSPs) whereas SCBCD focuses on the business tier (
EJB). There cannot be any recommended approach for taking one exam before the other. Ask your friend why he thinks
you should take SCBCD first?
Ask yourself why are you getting certified? what knowledge will be applicable to your daily activities right away - servlet/JSP or EJB? Do you develop multitier web based applications? In that case you can take either certifications first (provided you do EJB development).
I think SCWCD is easier but that's just my opinion.