The higher up on the pyramid the evidence, the better the evidence.
When using the word evidence - think of the word research or journal articles. The better type of research to answer a question, the better the answer.
Example:
You have a journal article about bruxism which is an RCT (Randomized Controlled Trial) and a Case series on bruxism. Which one is better? The RCT! Why? It's higher on the evidence pyramid.
There are many different kinds of EBM pyramids. This pyramid represents the basic model.
Decisions and Evidence in Medical Practice by 
Evidence-Based Medicine by