It seems as if everyone around here has used First Aid for Step 1. I have read it once but I am planning to read Step-Up for a final review. It seems much more complete than First Aid, except for Pharm in which I will review that in First Aid again.
I used step up. I agree that certain subjects seem more complete then first aid; and many people prefer the organ-systems approach. If you do purchase the book, I would just reccomend making sure that you either purchase the revised first edition or the second edition since the first edition is riddled with errors. It's an excellent comprehensive review book though, and one of my dean's actually reccomends it as an either step up or first aid book. I would definitely purchase first aid, but I also think that most people should try using step up too.