Having read both the Moss book and the Hunter/Crawford book, the Hunter/Crawford book takes Servlet programming to the next level.

I especially found the hints/tips on what works well with the Java Servlet API, and what doesn't very useful. The Servlet environment, Session Tracking, and Interservlet communication chapters have material you won't find elsewhere, and you'll keep going back to them for reference.

If you are thinking about writing Servlets for a living, I'd recommend both books (Moss and Hunter/Crawford). If you can only get one, this is the one to get first.