Personally I think Dearborn's materials are the best. Two reasons. First, they give you a ton of questions as you're going along. You may get 100 practice questions by the time you get through the chapter. I always heard how great STC is, but you only get 15-20 practice questions per chapter. You only get a bunch of pracice questions when you do the final exams. I think it's much more productive to reinforce your knowledge as you go along than to wait until you've studied the entire book.
Second, Dearborn has about 100 'test topic alerts' throughout the book. So you read a few paragraphs, you have no idea what nuggets you're supposed to pull out of it. Then you read the test topic alert, and it tells you what's important out of what you just read. Just reading and understanding these is probably good for about 75 questions.
What's really good is Dearborn's complete course on CD-Rom. About 2000 practice questions, and you can build an unlimited # of practice tests on any area(s) you want.