I have several friends who go through their own particular interests. Some enjoy reading stories, while others prefer to do research and follow charts. I will give you some insight as to how you can choose the best one for you.
First, I would say that you should focus more on the study guides and practice exams that focus on organic chemistry. These are two very different subjects. If you decide to take an exam that only focuses on the second subject, you will be wasting your time.
There are also guides that make you read a book. You need to study with the help of the books. The best way to do this is to use an online resource.
When you read the book, you have to use your own way of understanding. You will be working on two subjects at the same time. With these study guides, the most effective way to study is to read the materials and then work on the questions that interest you.
Lastly, you must choose which one you are going to do. The practice exams that you find on the Internet will give you a feel for what to expect when you sit for the real exam. The nice thing about these resources is that they allow you to download them so that you can take the exam any time you like.
It is always a good idea to go through each one of the practice exam available to see how they are laid out. Find out how they are labeled. What part of the exam are you studying?
Next, pay attention to how they word the questions. You will need to know the answer choices before taking the actual test. Also, you want to read over all of the questions thoroughly before taking the test.
Check to see if the test is covering specific passages that you do not understand. Ask yourself why you do not understand each passage. I always read through each question again to make sure that I understand it.
You should also check to see which tests have different resources. For example, some tests will allow you to search your answers in Google. Others will only let you search directly from the PDF file.
I always think that organic chemistry requires the most testing because you will be able to use multiple methods of learning. I think that the other tests may be less taxing because they only test you on the topic in order to get your grade. This does not mean that the other tests are not valid because they might give you a great idea of how to apply the material in class.
My advice is to find a place that has several of these practices available, and then choose the one that you want to take. Check to see how each one is laid out and then take the exam that you feel comfortable with. This way, you will be able to ace the exam.