I've went through CaseFiles, Beckmans, the two tests on ObGyn from the Kaplan question book, and all of the Uwise questions. I've also taken three tests from Kaplan for ObGyn residents.
I haven't taken the test yet, but I'm scoring 70-75% on the Kaplan Obgyn resident tests.
In my opinion, the Uwise questions have been the best. Casefiles was also very good and high yield, (but it is probably not enough on its own) and a really good supplement to Beckman. Kaplan was decent, but a little easier than I think the real test questions will be. Beckman's is too general and the questions are a joke. I didn't read blueprints, however, I think Beckman's was easy to read and a good overview; it just needs to be supplemented by a question bank.
However, I have done some of Pretest, and I have to say I think it sucks. A lot of the questions are obscurely worded which makes it difficult to understand what they are asking. I don't think it is high yield because I haven't learned much from the questions I got wrong.