HeadFirst is the best book for SCWCD.
In
your opinion, naturally
I would recommend checking the
SCWCD 5 Links, and before deciding to buy any resource (book, online resources, mock exams etc.), read the reviews and look at the TOCs, then decide which seem the best for you. Don't be afraid to get more than one if you can't decide - that's usually a good plan as you'll get many different views on the same topics which should really help to clear any misunderstandings.
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / Amazon Amazon UK )