Hi Steve,
I don't think there is a simple answer that suits everybody. Possibly one way to decide would be to base your decision around which part of the assignment you enjoyed the most. If you liked developing the client app, maybe work on SCWCD. If you liked doing the server side, maybe do SCBCD. Or if you liked creating an interface between the two (especially if you used the Command
Pattern), then maybe SCDJWS could be interesting for you.
One of the things I found helpful in my study was taking the SCJD assignment, and then using that as a base project to apply the techniques I was studying to. For example, while studying SCWCD I created a web front end that connected to the stock standard server I had created for my assignment.
Regards, Andrew