In my opinion, Chad's videos are the most effective method for learning the chemistry sections. Use the quizzes to reinforce the content, and write and rewrite his reaction sheets down until you lose the will to live (or your hand falls off, whichever happens first).
Chad's videos + quizzes for GChem and OChem perfectly align with the content that you need to know. Nothing extraneous was covered, and almost nothing was missing. He also has lots of good tricks to do math very quickly for GChem. Also, the types of questions you get are very, very similar to the real thing.
I had practically no recollection of either of the two subjects before I started studying - I hadn't taken Gen Chem for 7 years, and 5 years since I'd taken Organic. I got a C in Organic I. I had to take Organic II twice, earning only a C my second time. I used Chad's videos + quizzes + reaction sheets as my only material for about 6 weeks, and I added the OAT destroyer for the last week or so. I got a 400 on both sections.
Chad's videos and quizzes cover probably 29 of the 30 questions that you'll see for each section on the OAT. The OAT Destroyer becomes useful when you want to be sure you'll be prepared for all 30 questions, instead of 29 (28 if you're really unlucky). The Destroyer OChem road maps were also useful (especially to familiarize yourself with different ways of writing the same reagent/reaction).
Chad's was okay for the rest of the sections - except Biology, which simply weren't very useful at all. In order to minimize the amount of prep material, I used only Cliff's AP Biology to prepare for Biology. I took notes for a few hours a day for about a month. I ended up with a 380 in Biology (4 years since I had taken any Bio course). I found Cliff's to be effective in learning the relevant material and in helping focus on learning the material rather than juggling a bunch of different sources.
