World is a great question bank, as is Kaplan's QBook. But I didn't have those for the Shelf Exams. Here's my opinion:
Pre-Test: way too low-yield. Use it for studying, if questions are your thing, but not for gaging how well you'll do on the actual test.
Blueprints Q&A books: NOT the actual Blueprints texts, but the Q&A books they put out for Step 2 around 2006, are great, and I think they were close in difficulty to the actual Shelf exams. They make one for each subject, and your school library probably has them. Others may say otherwise, but I swear by them. So for practice, I say get these.
The text I studied from was Case Files early in my 3rd year, then First Aid for 2K and Kaplan later when I did IMED and FMED. Case Files for Surgery and Psych really helped me on those Shelf exams.
Jake