As has been said a few times before, which exams you go for should largely be a function of where you're going with your career and where you want to go.
If architecting software is something that interests you (or your job is heading in that direction), then SCEA is certainly a good option. If your job is going to utilize Web Services, then the SCDJWS is a good option.
I found that preparation for Part I wasn't all that long - perhaps a week or two of some review of the portions I felt unsure of. Part II took longer (and it always will) since it's a practical design assignment, and Part III's preparation is Part II.
Hope that helps!
